Sorry to hear about your plant dieing. We bought one of those kits similar to what you had and we had a hard time growing them too. There are a lot of ways to grow plants and each type of plant can be unique. Tomatoes I would reccomend you get your own pots and soil to start. Place the seeds 1/4" under the surface of the soil and place in awarm sunny place. Keep the soil damp to promote germination until the seeds sprout. Once they sprout you must be a little more particular with the sprouts. Too cold of a breeze, too stiff of a wind and they could die. Keep them in a well ventilated but wind restricted environment. (Anything similiar to a green house effect to stop the wind and keep them in a warm environment.) Once the seedlings are 2 weeks of age or so, you can give them a very mild amount of fertilizer to help give them a boost, From the time they sprout until they are 2 or 3 weeks old, overwatering will kill them very quickly as well so it is better to give them a "little" amount each day rather than water until they are "wet". You will find after they are about 6 to 8 inches tall and ready to plant outside, they become a lot easier to grow. I hope this helps and good luck!
GG131 My husband the green thumb.