Theres tons of strategies for leveling up the repair skill, I will be covering several effective methods. Also keep in mind you need an iron block for all of these methods (except one). Keep that in mind! If you are level 50 or higher, go to part 2 (If you're level 600 or higher check out part 3, but it's slower than most methods in part 2) of the guide! Otherwise, Let's get started.
Heres an experience chart for all materials per every time repaired(Results may vary, These numbers are not exact!):
Leather: 65 experience
Wood: 35 experience
Iron: 325 experience
Gold: 300 experience
Diamond: 2000 experience
String: 250 experience
(These of course are doubled with [VIP] powers!)


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Part 1 (Levels 1-50)
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     Since there are so many methods I'll be covering here I will actually be dividing them into subsections for part one. Again, although it's not listed, you need an iron block for every method! All of these methods can be used past level 50, but usually they won't be as effective, as you can repair diamond tools by that point. Here we go!

Miner's Method:
     Probably the most standard method but does get the job done. This is good for people looking to raise mining levels a lot, but also get some repair levels on the side.
Here's what you need:
-Iron Pickaxe
-Torches
-Iron Ingots
As simple as it gets, here is what you do:
1. Go to a level in which you want to mind, I recommend under layer 16, as there are diamonds to be found there, and mine in any pattern you want.
2. Mine until your pickaxe is near breaking point (One pixel on the bar should do).
3. Repair it on your anvil
4. Keep mining, and repeat the process.

     
     Like I said, the most standard method but hey, it works. You'll gain lots of ores, including iron, so you can't really lose money or resources with this method. You'll also gain mining levels, but yes this will take a while, probably the slowest logical method.

Speed Miner's Method:
     I'll warn you, this method is expensive to your resources.This is the method I used to get from level 1-50 though, as it may be the fastest method to get to level 50.
Here is what you need:
- Gold pickaxes (One will work, but it will be slow, I used a total of 25 pickaxes)
- Gold Ingots
- Torches
- Iron or Diamond Pickaxe (Optional: to mine ores such as iron or diamond, as the gold pickaxe cannot)
     Yep, that's right, gold! The reason this is the quickest is because gold breaks down crazy fast. Not only does it mine cobble faster than any pickaxe in the game, but it degrades very fast! Around 25 blocks before it hits no pixels fast. Combine those two together and you have a very quick method to level up repair.
Here is what you do:
1. Find a layer to mine on (same standards as the iron pickaxe method)
2. Mine with your gold pickaxe on stone blocks until it hits a black bar (No colored pixels showing)
3. Repeat step 2 for all your pickaxes
4. Repair all of them, with a repair level lower than 50 it should take 3 gold ingots to repair each one, around 900 experience per pickaxe! And 22500 experience for a trip!
5. Repeat the process, a pickaxe or two might break, just keep going in that case with the ones you got.


     This method is costly, because of the real lack of space you mine, you find little to no ores, meaning you pay for 98% of your levels, however I consider it the fastest, and if you're looking for speed this is your method.

Cactus Hugging Method:
     This one is a bit more painful. The method is actual very effective, but due to the heart loss, it tends to be slower than mining (due to time healing). This can also be effective with diamond armor! Let's get right into it!
Here's what you need:
- Armor of any kind, Gold is the most effective, as it degrades fastest, Iron is the second best.
- Cacti
- Sand
- Food (Golden Apples are very helpful)

     In place of Golden Apples a beacon with restoration works as well, but That is very expensive due to the beacon, and the blocks needed.
Here's what you do:
1. Set up a little "pain area" 3 cacti plants in a pattern so that there is one block in between all of the, as in the picture below.

2. Stand in between (red wool block) all 3 cacti plants, stand there until your armor is almost dead OR you have 1/2-2 hearts left.
3. Repair armor. Since armor takes more materials to craft, it also takes more materials to repair, giving more experience!
4. Repeat process.

      If you want to go real overkill, combine the golden apples with the beacon. You will almost never die. But if you're not rich you can always just do it the normal way with regular food, and wait for your health to regen.

Fishing Method:
     Yes I'll include this method, even though it's a total chance game when you use it. I'd only recommend this method if you also want to increase your fishing levels. But who am I to stop you? Here you go, fishermen.
Here's what you need:
- Fishing rod
- String (No matter what you will need this for the fishing rod repair)
- Assorted materials to repair with (It depends on fishing level really, you can fish up any armor or tool type, so bring all your iron, leather, string, cobblestone, wood, gold).
- A body of water
     
     If you wonder exactly what materials you need, you can check the mcmmo wiki, but some of the information may  be out-dated. Link here:http://mcmmo.wikia.com/wiki/Fishing
Here's what you need to do:
1. Find your spot to settle and fish.
2. Fish as you normally would
3. Whenever you get a damaged item, repair it.
4. Whenever your fishing rod is near dead, repair it.


     This method is similar to the first one. You gain lots of fishing levels, but repair is more of the side thing. If you're really aiming for repair levels, and only repair levels this method is not the one for you.

     Finally, level 50! It's time to repair diamonds! Oh boy, Diamonds! Part 2 coming your way!
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Part 2 (Levels 50-600)
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     Now that you have diamonds added to your repairing abilities, things are going to go quickly. Very quickly. Let's get started! (I think I'm saying things like that too much )

Tree Feller Method:
     This method is not for everyone sadly. It's a great method, but it's effective increase with your woodcutting level. Check out my woodcutting guide for more info on that here: http://www.noobscraft.com/guides/woodcutting-guide-(pictures-included!)/
     Another thing about this method is you virtually cannot lose money. It takes about 3 diamonds at max to repair a broken axe, and using tree feller will gain you more money from "/sell" than diamonds cost. And I suggest at least level 100 woodcutting before attempting this method. Now with that out of the way, we can start.
What you need:
-Diamond axe(s)
-Dirt
-Jungle Saplings (You'll get alot from this method, so don't start out with a bunch)
-Bonemeal (3 stacks should do fine)
-Space in a NON-SNOWY BIOME (The trees will now grow otherwise!)

      I'm running out of things to say here. Again, make sure you are in a non-snowy biome!

What you do:
1.Make serveral 2x2 dirt square for sapling placement, space them out at least four blocks. Here is a picture example:

2. Plant the saplings in a 2x2 square on about 3 of your dirt plots (For every 200 levels past 100, add 3 more spaces and a diamond axe (Example: level 300 woodcutting = 6 spaces and two diamond axes))
3. Grow the large jungle trees
   
4. Cut the trees, if you are using more than one axe, switch to another axe once one of your axes hits red-bar. If you do not the axe may break and you will lose it as well as your repair experience!

5.Collect jungle logs, you can turn them into planks and "/sell" for a nice profit if you want.
6. Repair axes, If you do it well enough with one axe you can make around 4000 experience every 3 minutes!

     Man, woodcutting and repair combined? What more can you ask for?! Maybe that's just me, but this is the quickest leveling of repair I know of. So this is your go-to method.

     With this method you will be AFK alot. So you will need a 3 minute activity to do while you're waiting if you don't want to stare at a timer. I personally watch videos, play around on forums, or play another game. But figure out what you want to do.
The next two methods are just diamond add-ons to previous methods I explained:

Diamond Pickaxe Mining:
     This is the same as the iron pickaxe method or Miner's Method, just with diamonds. Once again, good if you like leveling up mining primarily, It's honestly something if you don't want to level up woodcutting.

Diamond Cactus Hugging:
     This is the same thing as the Cactus hugging method, just with diamond armor. Do everything the same with diamond armor as before. Probably the best alternative to the Tree Feller Method.

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Part 3 (600+)
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     This is more of a bonus method to be honest. It's good for excess materials, but like the Tree feller method, it's only useful if you have high fishing stats. Here we go
What you need:
-Gold Block
-Fishing Rod
-Various materials to repair (Yes you do need to repair the items you fish up before you salvage, as you can only salvage when the item is at full durability)
-String

     The gold block is needed for this method, as it is used for salvaging. This method can actually gain a bit of profit too!
What you need to do:
1. Find a body of water for fishing.
2. Fish until you get some repairable items.
3. Repair the items to full durability on your anvil.
4. Salvage them for their resources on your gold anvil.
5. Repair fishing rod when needed.


     And that's it. Although it's actually slower than the Tree Feller method it's something. I personally am not to big on fishing but, meh. You guys can test this method and see how you like it.

     Well it's been wonderful making this guide. I hope it helps you get up to a desired repair level. Have fun!:3

-Suppusmac