If you want the nice bars then head to bedford place at the top of London road. You have Lizard lounge, Mono, Orange Rooms and Apartment 26. All quite swanky up that end. You also have wetherspoons pub on London Road (called Giddybridge) which is cheap and doesnt have loud music.
I usually start in London road, do a few bars there and head down to leisure world to bambuu as I like RnB. Not sure where the house clubs are in soton tbh so maybe someone else can help you out there!
If you dont want agro then avoid Kellys club! Its chav central there and I've only been twice and seen fights both times!
Club wise if you want so disco style 60s music with an age range of 18-60 where you can do daughter, mum and grandmum all in one night, head to Flares!
There are also smaller clubs dotted around town. Academy is a studenty club but as its not term time I cant see many students being in there. You also have Nexus which plays rock/indie usually. Clowns/Jesters is a hole (but dirt cheap) again a student place so not sure its even open at the mo.
A few of the bars have late licences too with a dance floor if you dont fancy a full on club. Just dont forget southampton is pretty lame so most bars dont stay open past 12 and the rest all close by 2 or 3 it seems. Only a few stay open later. Bournemouth *** on this one!!
The 3 main clubs are down in Leisure World (where Odeon is). Bit of a trek from london road but then again southampton is spread out anyway. You Ikon/Diva, Jumpin Jaks and Bambuu bar there. Bambuu is RnB/Rap stylee music. Ikon/Diva changes so no idea whats on in there. Jumpin Jaks is full of slappers in short skirts
Oh yeah, dress code wise anything seems to go nowadays!! Just wear a shirt, jeans and shoes or smart trainers and you're sorted.