You can always add water or fertilizer, you can always prune, but you can't change soil under a plant or add sunlight.
So plan before you plant - pay good attention to WHERE you are placing your plants. Know what kind of soil you have (Heavy clay? Sand? Organic loam? Acidic? Rocky and basic?) and what kind of exposure (Direct, all day sun? Partial shade in the afternoon? Cold shade all day?) It sounds complicated, but really it only takes a few minutes observation around your yard over the course of a day to get these details. You can purchase soil testing kits pretty cheap or, if you are hard-core, take soil samples and have it professionally done at your university extension.
Then use that information to decide where and what to plant. Sunflowers won't grow big and tall in that moist shady spot under the eaves. Ferns will shrivel up and die in the hot sun against your southern wall. Carrots won't grow well in hard clay.
If you need help figuring out what goes where, just ask at your local nursery. They will know your climate (and probably local soil types too) very well and will be full of good advice.