Some of the best YouTubers have all kinds of strategies, and some of them are nuts, while others are pretty good. If you are a low level, don't attempt any of these load outs, like CosmicDuo's all Smokey Warrior charge. Just stick with Heavy Zooka or Heavy Riflemen. These two combos work best against Sniper Towers and Mortars. With Machine Guns, make sure to bring more than one Heavy for damage absorption, even if that means upgrading your Landing Craft. If you want to succeed, follow my advice.
1. Never charge a Mortar head on with the Hooka. The shells will wreck your Zookas before they lay a finger on the Mortar.
2. Don't waste GBE. Even if that means letting that Sniper Tower fire on your troops, don't fire on it and let the Cannon right behind wreck you. Use GBE on Flares, Artillery and Shocks.
3. If there's a base you think you can destroy, ATTACK IT! I've seen too many times people not attacking bases that are so easy. Just clear your map so you can focus on Dr.T and such.
4. Upgrade your troops and GB abilities. After that, you can assault tougher targets with ease.
5. Try to encircle the base.