Besides the attacking tips , this is a small trick for people who have really low level (about level 7-10). This can help you raid any level 3-4 star base effectively if the right units are placed in the right place. And just in case you loot a few resources, remember that the cost for coins is very low and a only a few thousand resources will be used.
Attacking with a bunch of marines
Marines are the first troops a user gets in the game and definitely the best strategy for an effective starter raid. I have tried the tactic of training 64 marines but this strategy will not do the complete destruction of the planet. The trick is to use 32 flamethrowers and 32 marines (this will work if you have two warpgates level 3). (P.S. Your marines level should be at least level 2 or higher, level 3 is recommended)
Adding flamethrowers to the mix
Flamethrowers only attack defenses and are only 250 coins at most. So they are really good at destroying sniper towers and laser turrets if put in high numbers. So if you want to destroy all the turrets first just put about 32 - 64 flamethrowers on the planet and watch the mass destruction of the planet. And be careful with cannon blasts if your marines and flamethrowers health is low.
First just distract the cannon blast by putting 6 marines on either side of it.
Before the marines are destroyed throw some flame throwers right behind it the flamethrowers best interest are turrets so they will destroy it completely.
Now focus on the laser turrets. If you like just put a few beetle tanks and bazookas or just follow the same thing as for th cannon blasts.
Freeze turrets and missile launchers are no problem if you destroy all the other turrets (sniper, cannon and laser) and only have ground units. and if you do have air units, just destroy the missile luancher with a few ground units then go on and attack with your air units.
(Note: Mortars aren't found on level 4 star bases so they are no problem.)
Once all the turrets are destroyed just deploy all the units you've got and the planet will be completely destroyed.
(Sometimes a few looters can help loot resources when all turrets are either destroyed or distracted. )
Now go out and raid some planets, and watch out for traps!