Exposure to sunlight cannot be stressed enough. This can be either artificial or natural, but the more of it your tomatoes can get the higher yield you can expect to have. So to ensure that your young tomato plants get the light they need to grow, it is recommended that you put them under grow lights. Then once they have a good start you can take them outside. Then you can put them in a part of the garden where you know they will receive plenty of natural sunlight.
Any of the tomato growing experts will tell you that your tomatoes grow best under conditions of warmth. Before you ever start your tomatoes one good tip is to first cover or enclose the part of your garden you plan to use and heat it. This can take you as long as several weeks which is why early planning needs to take place. Warming up your garden spot is not a guarantee of juicy tomatoes, but it actually does accelerate the speed for their growth. This alone makes it worth doing.
A common mistake many gardeners make is to crowd their seedling so they can get a higher yield. I will let you know right now that this may get you some more tomatoes, but you lose a lot in quality. Tomato gardening works at its best when you space out your seedlings to let them have enough room and to spread out. While they continue to grow some experts recommend that you move them to a larger place that will further facilitate their growth and give them enough space to grow to their full size.
Another tip for your tomato gardening is fanning your seedlings. It's not really clear why this works but it is a common belief that tomato plants will grow better when placed under a constant light breeze. It might be that a breeze forces your plants to develop stronger stems. You won't need to keep a fan on them all day, but just half an hour a day should be sufficient.