Combat practice probably best done by dropping into any old NAV beacon and scanning ships that spawn in to see if they are wanted and have a go at them. In normal NAV beacons the skill of the AI ships is average. As you step up in skill you'll want to find "Compromised NAV beacons", it will say the the name if it is a compromised one, I think EDDB.com will list these as well. In these nav beacons the AI skill level is considerably higher. You can also just drop into resource sites and go after pirates, but nav beacons are somewhat better IMO due to the lack of asteroids in the way.