Build your turrets with overlapping areas of fire. This will help later in the game when you need to defend your base from attacks.
Be sure to upgrade your bank early on in the game. Many of the early / training missions pay out a decent coin reward, and if you don't have the storage capacity for the currency, you will lose it.
Recycle as many of the plants from around your base as possible. While they do provide obstacles for invaders to overcome, they also provide (visual) cover for them to hide under.