all the pipes go in before soldering, else some solder might run into the other ends and you wont get the pipe in! Do them all at once and use plenty flux.
heat the pipe and not the fitting with yorkie fittings, take the heat off when you get the first showing of the "silver ring" Straights and bends are easier than tees to get a nice looking finish with as you are only heating two sides. Always clean your joints afterwards with a damp cloth to...