Well the first thing I would suggest is the lowest ISO you have.  Secondly a cable release is an absolute must,  if using a low iso, because shutter speeds will be slow.  I know the more modern cameras have high usable iso's but the low iso/shutter speeds will give a more ethereal water and atmosphere too.  If you'd like star lights on the point sources of light, ie street lamps etc.  Choose a smallish aperture. 

I like to shoot ISO 50 f/22.  gives a long shutter time on the "Bulb" setting of the camera.  And also helps to create better star-bursts on lights.   I usually start at 15 seconds, and if it looks too dark, start going a bit longer.   If you can't get down to 50 then iso 100 and obviously double the shutter time.  I have had on occasions a whole minute :)  Also shooting in RAW helps, so you can rescue and blown highlights in raw post.  It's all suck it and see really sweetie.  The rule book will tell you f/11 and it's corresponding shutter speed via aperture priority.  But I do prefer the bulb setting method.  Up to you really.