Know where your sun /shade is, and pick the right plant for the right place.
Start small, read everything you can and ask other gardeners their advice to learn more.
Putting a single tomato plant in a big pot, with fresh soil (bagged, not from your garden) can be very successful--cherry or grape tomatoes are perfect for this. Pinch out the suckers so it grows tall, not wide (the suckers are the little leaves that start at the junction of an existing leaf). Water daily, and feed every week two.