I use 63/37 solder and kester 951 no clean flux. The extra flux will make a huge difference in the quality of the solder work when working with such small components. I use a tip that has a width of at least half as wide as the pad. The smaller the tip the slower the heat heat transfer rate. The tip size will determine the temperature you will need to solder. The smalller the tip the more heat you will need to melt the solder because of the slower transfer rate. It is better to have the contact last no longer than 2 secs [at 350C] with the pad to prevent damage to the circuit board. Make sure to clean the old solder off of the pad before resoldering. Adding the extra flux gives an extra bit of "wetability" it allows the solder to stick better and give flatter smoother solder joints as well as helps with bridging issues.