first u need a supply depot at ure 7th SCV
Second u need a Barracks at ure 9th SCV
third a second barracks with the 10 th SCV
4th u need a refinery make with tenth SCV
5 make another SCV and get an acedemy with it
send the 11th scv to mine gas
make sure ure making mareines the whole time as ore permitts
then u make at least 4 medics and attack the least defended area of the enemies base ie gas mine usually not covered if there is a bunker or cannon in the choke point take it out first u should have atleast 8 to 12 marines and 4 or more medics make sure that u control the medics seperately so they dont wonder off!!!! meanwhile back at ure base be sure to keep climbing the tech tree. (tip: first up grade marine range!!)

CreepColony's Opinion: Marine/medic attacks are funny, because medics act weird. They'll wonder off and heal each other, heal your allies, and not cooperate. I find that a good way to make medics do what you want is hotkey some marines 1, some medics 2, and some more marines 3. Then press 1, a (somewhere), 2, a (heal, somewhere), 3, a (somewhere), and then press 1 and t (stimpack) and 2 and t. This will force the medics to heal your marines, so some heal the ones in front of them, and some heal the ones in back of them. Get it?