I have found the awesome guide to farming. I Want to share it with you. I hope it'll be useful for you and help spend less troops, gold and nerves ;) 

Yielding speed

The level of a Resource spot gives how fast you can farm it. A level 1 tile (spot) of Iron gives 16k/hour compared with a level 6 tile that will yield 129k/h. For Lumber/Stone you get 173k/h on a level 6 tile.

Level 5 and 6 tiles are much faster than level 4 (and lower) tiles.

Yielding speed can be boosted by Hero skills, Knowledge and by special Hero Equipment. Your hero must accompany your troop to use the speedup from Hero skills.

It does not make any speed difference based on what type of troops you are farming with.

Gold tiles gives 6 coins/hour regardless of tile level. By Gold knowledge you can speedup this by 10%. Spending time on farming gold is possibly the worst you can do with your time, except if you are hard pressed for gaining a few extra gold coins.

There are also daily events that gives 10% faster yield on Mondays and Thursdays.

Competitions

Sometimes there are Competitions where you can win some nice stuff. In some of them you earn points by farming resources.

If you are farming because you need to gain competition points as quickly as possible, prioritize as follows: 1. Food, 2&3 Stone/Lumber, 4. Silver, 5. Iron. Silver is half speed compared with stone, but gives 2x points.

Kingdom vs Kingdom Competition

In the Kingdom's battle you can earn KvK points by farming in the other Kingdom. No KvK points will be given when farmin in your own Kingdom.

If your Kingdom wins the competition your Kingdom will get a special Resource tile called Gold of Gods which are active during 5 days from the end of the KvK. These gold tiles give 1 gold/minute (regardless if level 6 or level 1) and can be worth spending some time to farm (as opposed to ordinary gold tiles).

Capacity

Troops with higher "tier" (t3s-t4s are highest that you should send, but the best choice will be t1s. If they will be killed you lose less.) can carry more but are much slower when marching to/from a tile, t6 are the mosts slows.

Quickest are Horsemen (t1s) and any type of Cavalery. Slowest type are Siege but these have the best capacity. To farm the same amount of a resource as 22k of Trebuchet (t1s) troops you will need 40k of Horsemen. Thus, if farming is your primary objective, Siege are a good choise. Horsemen are a good second choise since they really make things up by be quick to move around. To balance up for the poor capacity you just use more of them.

Capacity can be boosted by Hero Equipment and by the Capacity knowlede. On Thurdays there is a Daily Event that gives you a 10% increased capacity.

By using a Troop Enlargement booster you can send more troops than your maximum troop limit allows. You must however posses these troops - this booster does NOT make your troop bigger, it only allows you to send bigger troops if you have those soldiers.

Farming with a Hero

When the Hero accompany the farming troop, the Hero skills and the bonuses added by the Equipment the Hero is wearing are applied. By using Hero´s Double you can send the Hero with two farming parties at the same time (but in a hostile environment it can be better to leave one of them at home to help protect the town).

By farming two different tiles at the same time you farm faster than if sending all troops to a single tile.

The Hero may also give extra defence bonuses if you are attacked on a tile.

Include Hero in the party that are about to farm the biggest loot, it makes that go faster and fewer troops are needed.

Attacking the Resource spot

To find a good tile near you, you can use the Watchtower. Do NOT "attack" a resource spot directly from the watchtower - always goto the tile and make sure nobody else are already attacking this spot.

If you have mixed types of troops available send the faster ones to the tiles further away and send the slower to spots nearby.

Tips: Try to attack tiles directly at your west/east (left/right) direction from your town - your troops will travel twice as fast as if they where to travel in the north/south (up/down) direction on the Global Map.

By moving quickly you may lessen the risk that an enemy happens to see your movement, which is important in a hostile area.

You can apply a Timed Marching Speed-up before you start moving to a resource tile to increase the marching speed by 50, 100 or 200% during a limited time. Since most time spen when farming are not the marching part, this is of limited use.

During a march to the tile you may apply a Marching Speed-up Booster that shortens the marching time currently left by a percentage amount.

If your are about to really attack an enemy that has occupied a resource spot, this is another course .

Farming in a hostile area

Since the other course does not exist we continue with some stuff that regards this too.

If your are in an area where you have the risk of beeing attacked there is some extra things to think about:

If you farm on several nearby resource tiles you can watch them all and maybe get time to withdraw your troops in time if attacked.

If your tiles are further apart it is harder for an enemy to port in an hit everyone quickly.

Only farm with t1s! These are easy to replace and will give the attacker less points. In this scenario the Trebuchet are the ideal farming troop. These have good capacity (less troops needed and thus less exposure)

Farm with smaller groups, not more troop than you can afford to loose. You'll always get hit now and then (if tile hitting are allowed) so it is just the price for doing buisness. You can even train new troops before you lose the current :)

The rules about rss tile hitting varies between Kingdoms and Clans, so you must check the local rules yourself.

Scouting

Beware that you will never notice if someone scouts you on a resource spot. You will only be notified that you've been scouted if you have one or more scouts, but since you can not bring scouts on a farming trip, you'll never notice.

If you like to scout someone else on a resource spot, it is enough to send just one scout. Scouting always succed and only the one scouting will know about it (and his clan fellows who can see the result in the clan battle log). Note that the coordinates shown in the clan battle log (when scouting a resource spot) are not revealed, instead the coordinates to the targets town are shown. In the mail sent to the scouter the correct coordinates are given.

Shielding

When your town are shielded you can not attack an occupied resource spot. If the spot is unoccupied but someone else reaches it before you do, the troop will return without trying to take the resource spot when it arrive.

If you are shileded and need to get som kill enemy points in a competition you can farm and hope someone hits you (even if most of your troops die, you usually get one or two points on the other guy which makes you in on the prizes. Or you can try to insert your troops before someone else (unshileded) reaches the spot, in which case you may be able to use enough big troops to beat the other guy.