As you could understand, there are two sides in the game: attack and defence.
Someone could prefer attack someone else could prefer defence, but at the end of all you will need to do both to have the maximum experience in the game!
However, talking about attacking and if you really want to go through this road, you will need to upgrade your Wizard’s Tower and your Troop Academy as priority buildings. Spells and Troops are the main protagonists of a raid, and have them at very high level can help you a lot during the fight, especially also if you have Elite Boost Troops. Each player has its own base design and its own troops/towers defence so sometimes it is essential swipe from a spell to another to be able to raid him/her at 100%.
An advice is that if you see in the minimap of the player that you are going to attack, many range troops (that could be Arblaster, archers or mortars, etc.); go for high range spells like Swordrain, Blizzard, etc. because most probably he/she will use many or long chokepoints.
Instead if the base you are going to attack has low range troops or towers (Frost Towers or Gargoyle Tower, etc.), use short spell like Hammerstrike, Bladestorm, etc. or also high range spell.
All spells like all troops are good but some are more useful than others. About spells, you should target on some specific spells to upgrade as:
Hammerstrike is a very useful spell that you can use for low, mid and high level gameplay. Thanks for its very low cool down (only 7 seconds) and thanks to its instant hit, it can reveal a very painful spell against most of units and towers (which suffer of blunt damage).
Swordrain already at level 8-9 can kill lot of troops in one shot but it is useless against towers, so the main reason that you should equip Swordrain in your arsenal is because the enemies’ base has lot of range troops that can make some problems. In this case, Swordrain is perfect to use.
Blizzard is important only in some cases, you will see that as soon as you will grow up with trophies you will meet also strong players and you will see more often Skull Towers. Skull Tower is very deadly but like all things, it has its weakness: Ice. Blizzard works perfect against Skull Towers but only at last levels because also in the same time it can almost kill other deadly enemies’ troops. My suggestion is to upgrade it lately when you have already other strong spells at mid-high levels.
Shield is perfect to save yourself and your troops in many cases. Even if it cannot do nothing because it doesn’t attack anything, its power of put a shield on troops and king is very dedicated. The best tip to full use this spell is create a group of troops all around you (also at start of the match using the scream of the hero to attract troops) and cast immediately Shield. You will see that you and your troops will live longer than before and you will be able to reach the castle also with more troops than usual!
Bladestorm is good versus all type of troops, a bit less versus towers, but upgrade it at a good level 5-6, do not remove it until you do not have a better spell to put in your arsenal.
Sonic Blast is perfect in every situation and every single gold to upgrade it (because it is the most expensive spell) worth to spend. Although it kills things slowly, its 3 seconds of activity, you can “Touch & Go” other towers or troops and kill them like you casted it for the first time and it will remove lot of health even if you arrive a bit late!
The other spells of which I have not talked (Toxic Cloud, Stun, Firestorm and Heal) can be upgraded in a moment later.
Now for attacking troops I personally suggest to upgrade and use:
Knight is the cheapest unit but also fast so it worth to use in each difficulty. You just need to know how to control them! For example use Scream if they are too far from you.
Archer is good in each case at start of the game for their range but later Arblaster could replace their job if not boosted as well.
Froster is very important when you are facing lot of chokepoints where other enemies’ troops are killing you from the other side. They can slowdown everything but they required a bit time to destroy towers.
Cannon as normal troops is able to deduct lot of health from towers (because cannon attacks only towers and obstacles) but are very weak from I would say all type of damage so they need to be always protected in one way or another.
In a moment later when you will have Elite Boosts activated for them if you are in an alliance that have them you can use:
Knight – Blazing Knight: a lot powerful against Tough Barricade and can become a second shield for you if you cast Shield on them.
Archer – Power Archer: very deadly against everything thanks to their blunt damage, worth to use with Elite Knight to make a great combo of an unstoppable army.
Froster – DragoFroster into Ice Dragon: Useful against any type of troop/tower/obstacle weak to ice (example skull towers or against gargoyle tower or blockade)
Pyromancer – Dracomancer: Same as the other Ice Dragon, Dracomancer when evolve into Fire Dragon is useful against any type of troop/tower/obstacle weak to fire (example Arrow Tower or Froster or barricade)
Cannon – Storm Cannon: Fast speed but worth to use it to destroy quickly all type of towers it will meet.
Surprise Mummy: thanks to its spawn of Knight or Elite knight (if the alliance have them activated), it can reveal a big help during some difficult raids where you are not able to pass.
Raging Wolf: have it in your arsenal it’s like have a free Battlecry every time it howls your troops making them resistant to all type of damages adding more speed to their attack and more strong than normal.
These are the main attacking spells and troops that I suggest to use from the beginning especially the first listed and go up with the others lately when your king will be strong enough to use them or when you will have the opportunity.
In addition, the other troops can be freely upgraded later when you are done with the units listed above.