For SMT soldering, you need the finest soldering point, and finest solder that you can lay your hands on. Usually very fine solder doesn't have a flux core, so you also need a flux pen.
First, paint the pads with a small amount of flux, then position the device. If necessary, you can hold it in place by pressing gently on it with a pair of tweezers. Solder opposite corners first - this will hold the device in place, then you can solder the other connections. Be careful not to heat the tracks too much, or they will lift off the board.