Designing an Army Composition
1. First Step
When designing an army, first you must decide whether you are going to create a farming, hybrid or trophy hunting army. It is also useful to have an army planner open while you are doing this. I recommend using the one on www.clashingtools.com.
2. Creating a Farming Army
To be honest, farming is not my area of expertise. However, there are many other guides on great farming armies like BAM, Barch, and WB/Giant/Tier1. Farming armies are mostly designed to get as much loot as possible, without caring about trophies. There are two different types of farming armies. Farming armies usually carry 1 rage spell and the rest lightning.
The first is a Hit and Run kind of strategy, which is designed to get a little amount of resources from collectors with as little troops as possible. This raid style is very time consuming because while you are attacking and using troops, new ones are being created, so you always have a supply of troops. tier 1 are the most common troops for this.
The second is designed to get a large amount of resources, but are still relatively cheap. These attacks usually have a meat shield such as giants and barbarians, and wall breakers to create gaps in the walls as a way to get to the storage for the goblins and defenses for the giants. The giants go through first and are followed by usually goblins and archers.
Some farmers don't even attack. They just leave their town hall outside their base to get shields. While they have their shield they just let their collectors do all the work. However, this way of farming does not produce many resources, even though you don't have to spend anything.
3. Creating a Hybrid Army
This is by far the most common army composition. Hybrid armies are designed to both win the battle to get as many stars as you can and win a lot of resources. Giant/Healers, Hogs with a few dragons, and a less expensive Balloonion are the most common hybrid armies I have seen.
Hybrid armies shouldn't be too expensive, but should be able to 2-3 star a base every time and get the loot while they're at it. These armies should range from 100k to 200k in elixir and 0 to 500 in dark elixir.
Hybrid armies typically have a good amount of units anywhere from 10 to 30 that target defenses and act as a meat shield such as giants, hogs, and balloons. These units are followed by any specialty units needed for the army such as wall breakers and healers for giants. Any hybrid army should also have troops to draw out the barb king and clan castle troops such as archers, barbarians, and wizards. One or two giants can also be used to get close to the walls and last long enough to draw out clan castle troops if the castle is centered. The final troop component are the damaging troops. These follow up the meat shield and destroy everything left behind. These troops can be archers, wizards, minions, dragons, and anything else that does a good amount of damage.
A hybrid army's spells are usually lightning, heal, or rage spells. Lightning spells are good for taking out clan castle troops if there is one, or taking out mortars or an air defense depending on your army. Heal spells are good for hogs, balloonion, and giants when they are getting low and hit by splash damage. Rage spells are good for the above armies also.
4. Creating a Trophy Army
Trophy armies only aim is to get as many stars as possible on a base with no cares of resources. The most common trophy armies are GoWiPe, all dragon, balloonion, hogs, and golems witch.
Trophy armies have a wide variety. Because resources are not an issue in creating a trophy army, anything can be used. Golems along with P.E.K.K.A's are pretty common as a meat shield for troops like wizards and witches. A few barbs and archers are still used to lure out barb and archer heroes and CC troops, but not much else. Trophy armies usually contain a much higher concentration of troops than in other armies, and usually wont carry more than 4 different troops.
All spells are used in trophy hunting, except for lightning spells. Heal and rage spells are used as stated in the hybrid army section. Jump spells are used mostly for golems to jump over walls and sometimes P.E.K.K.A's. Freeze spells are mostly used on inferno towers, x-bows, and sometimes air defense for hogs and sometimes witches.
Up until about crystal league, it is easier to just snipe town halls with a few archers than to spend hours creating an army. Don't waste your time.
5. Don't Give Up!
Don't give up just because the army you tried doesn't work. Watch the replay see what worked and didn't work. However, don't change anything until you have tried at least one other base, because not all are the same. Once you have done a few battles, make some tweaks to fix your army's weaknesses and try again.
6. Thank You!
Thanks for reading this whole guide (I know it was pretty long). Any questions, ask, any comments, tell me. I am open to any criticism you have.