I typically do something like this:
9/21/0 or 5/25/0, depending on team's damage output. Usually 9/21/0, cause the early ad is always nice. Runes are 4% lifesteal, one ad quint, ad or armor pen reds, flat armor yellows, scaling and flat mr blues.
Start dorans shield, rush either negatron or chainvest depending on lane matchup. First item is either sunfire or spirit visage. Complete the other next. Build either trinity or botrk if tanky enough, depending on needs. Botrk works well in current meta, so I normally run that. If not tanky enough, randuin's for ad, maw or wit's for ap.
Ult enemy tanks, bite everything, pillar to defend your squish from divers, or isolate targets for your team.