Ok, first get mining right away then u train as many SCVs as you can until u have 6 mining minerals. build 2 more then build 2 supply depots. then build SCVs until u have 12 mining. while your building SCVs start building Barracks keep on building untill you have 2 then build marines while you build more barracks move your marines to your entrance while u do (always have at least 1 barrack building a marine). keep on building barracks until u have about 6-8 and 6-10 depots. and NEVER build bunkers if using this strategy. keep on pumping out marines until you have u think you have enuf to attack. it would help to send an SCV to find there base. attack if you have alot of marines you should overrun them and if things last longet then 5min build an gyser and and an academy so you can research stimpacks and UED-shells. ill tell you how it would work against the races.
TERRAN-try to attack them early before they get tanks and your main target would be berracks (if they dont have a factory) so they cant renforce there troops after you destroy there berracks. this should crimple them. then after that hurry up and go into the middle of there mining operation and kill as many SCVs as you can. after you do this victory is secure. and always keep on sending your merines to there base to renforce your other troops.
ZERG- the only chalinging part in this is to build merines before they can rush u with zerglings. so hurry up and build an berracks as fast as u can. sometimes when im against an good rusher i build 1 bunker just to stall them from entering. once you have alot of merines you should attack if you have swarms of merines you should take the zerg out with ease cause you merines will kill most of the zerglins before they get to your merines.
PROTOSS- merine rush wont work as well against the protoss because of there sheilds. the main objuective is to attack the protoss before they get cannions. but if they get cannions you should attack they pylon so they get disabled then its all easy after that and stimpacks will work well against them too.