green house soil

If it is just plain garden soil and has nothing done to it, you need to dig in plenty of well rotted manure and dig it atleast a spades depth or more (but not bring any clay up or chalk) to encourage the roots to go down and also encourage worms up help incorporate the manure. Blood fish and bone can also be applied, but its getting the soil to a broken down, crumbly well dug state thats important. Remove weeds and plant away!
After a few years, the soil may become unusable as it may get old and also harbour disease- especially if tomatoes get blight and will need to be dug out, disposed of and new soil bough it.