Be assertive, but sensible. Don't hide away in the gutter - ride a couple of feet from the pavement, as it makes you more visible and cars will be forced to either wait behind you properly or overtake you, hopefully in a sensible fashion. In terms of busy junctions, take them slowly, and if you have to, just get off and walk round them on the pavement. If you plan your routes ahead of time, it can be worth looking at junctions with Google Streetview so you can see what things will look like. Pay attention to street signs and lane markings and get in the right lane in plenty of time. I'd be hesitant about squeezing through traffic too much. If there is one of those blocks at the head of the junction for cyclists, then by all means work your way up to it, otherwise it can be as well to just take a position in your lane behind a car. That's definitely a time when you don't want to be sat right in the gutter or between two lanes, because then cars will squeeze past you as they move off.
There's a lot more to it, but that's my brief answers to your questions... I'm sure other people can help out. There's some book that I recall Asprilla recommending... Is it called Cyclecraft? Yes,
here you go. That might be worth a look.