if your right handed what the fook are you doing as a southpaw? you should be orthadox, you have your strongest hand at the back, so you should stand left hand forward. your not trying to be rocky are you? cause it wont help you atall!
you need the strongest hand (your right) to be at the back so you can turn the whole body weight into it.

but... it all depends on your opponents fighting style. if hes agressive as hell, your gonna want to be more defensive, circling away from that stronger right hand.
however, you say your 5ft 3 which is fairly short (dont worry im a short ass too) you might not be able to stik on the outside, cause your opponent is likely to have better range than you.
get that footwork to a fine art. when the throws straight shots slip inside and work him t the body. you have to make sure your guard is fully up as you move away from him, otherwise your gonna get popped right in the chops!
after a couple of them hes gonna be sucking in wind like a proverbiable hoover, and thats when you can start to form an offense.

defensive people are a bitch, and if hes trying to counterpunch you have a problem.
try to establish eye contanct with him, then go for the oldest trick in the book, look at his body and punch to the head! fake some jabs to open up his defense and get in there hard and fast. once you got him where you want him, keep punching, and moving to his left hand side!

hope this helps, and if you got more info on your partner, give me a shout.

alex