This strategy is an all-purpose one (unless your opponent has 6+ siege tanks all in the one place that you attack). Get your mining going by whatever means possible and get at least one scv mining gas. Build 1-4 barracks and an academy. Now make 6 marines, 3 firebats, and 3 medics per hotkey squadron. Once you have made 8 squadrons (this will take up a lot of supplies), upgraded your infantry armor to AT LEAST level 1, and hotkeyed all 8 groups, send them all over to the enemy base. The medics keep your troops alive surprisingly well, while the marines can take on ground and air and the firebats can roast some buildings. I've found this strategy surprisingly effective; just don't use it when the enemy has siege tanks trained on your squads...that doesn't work quite so well.

CreepColony's Opinion: I think you'll have to have infantry armor and weapons at least at level 2. And it may be better not to hotkey your marines/firebats with the medics, because then you won't be able to stimpack them easily.