I just wanted to 100% agree with trag's advice about flux. I'm fairly new to soldering, but my experience is it never hurts to add flux (as long as you clean it afterward if it's corrosive and/or conductive) and it always makes soldering easier. I try to use no-clean flux so that there's no risk of future damage though (but I still clean it off afterward).

Generally if I'm soldering something like a through hole component, the solder I apply contains enough flux to do the job and I don't have to add extra flux if I don't want to. Even when I solder a surface mount capacitor or resistor it usually works fine too--but the soldering process is much easier and quicker if I add some flux first, so I generally add it anyway.

If I'm doing something smaller scale (like soldering a small chip with tiny closely-spaced leads into place), I *have* to add extra flux before soldering or else it will be nearly impossible to get the solder to flow and even when it does, there will be bridges across the pins.

The moral of this story: if in doubt, use flux