Before you move tomato plants outdoors, you will need to ‘harden’ them off. For more information on hardening off your plants see: Growing Tomatoes: Step 2 (Growing from Seed).
For information on choosing a variety of tomato to grow, see: Growing Tomatoes: Step 1 (choosing).
You should acquire your seeds from a reputable source. As tomato seeds age, their chance of germinating decreases.