Hawkson, you have so many options it ain't funny.
you will only learn by going to a school and practising with real people, the more real the better, you therefore have to pick a school that has some good instructor and good systems
you will probably need to expose yourself to 2 fighting systems to be well rounded
you should make rapid progress in a pretty short time, going from zero experience to some experience is a quantum leap, the rest is pretty much icing on the cake
Personally I think you should take a look at a few instructional dvds to get an idea of what a style is like, and also check out the schools in person and see what they are like too.
I personally think Bas Ruttens' dvds are good, his style is practical, useful in the street, useful if you are a big kind of guy too.
Whatever you do, you must know how to strike hard against a bag, how to avoid being hit, how to grapple / wrestle, how to handle going on the ground and getting up again fast, how to actually face off against a person (sparring), how to break holds / deal with unexpected shite that happens e.g getting tackled / rushed out of the blue.
I doubt I covered everything.
The ideal real fighting situation goes like this:
idiot(s) attacks you often for no apparent reason, and you are drunk, tired, otherwise distracted
you INSTINCTIVELY react in a way that disarms their initial, unexpected rush at you, because you have trained repeatedly to react that way. Man, you don't even know what the f#$k is happening at this stage
you reposition yourself in a better way, ready to handle whatever is happening next (or run if you can / want)
if you decide to attack, you do so with uttermost initiative with the intention of rapidly disabling the attacker(s). In my opinion the best thing is anything that puts them on the ground and keeps you on your feet, unless there are multiple people in which case using them as a shield is a good idea
you then escape if you can, it is good to be able to run fast. Note you can't always because what if you are with your ladyfriend. In which case shout for police or security, which if it doesn't get help, or frighten them off, at least looks good in a court of law
of course every situation is different. sometimes the guy might just be a drunk bugger having a go, in which case you can disarm him with a comment "man that was a good punch!" or some other charm, it really depends on the situation. people do some dumbass things when drunk.