I solder fairly regularly at work. I use a Weller WD1, which is a great iron but probably a little expensive for an occasional DIYer.

Also use Kester solder, w/rosin core. Believe this solder has lead in it, have used high quality "audiophile grade" lead free, silver solder in the past, harder to work with (as it requires more heat) but not bad if you have some soldering experience.

I hardly ever use additional flux, as it's typically not required.

I have a number of different tip sizes, depending on what I'm trying to solder.

Typically if your having issues with solder, your not getting the parts hot enough or you have a bad tip.

If you get a new tip, tin it (ie coat it with solder & wipe off the excess with a wet sponge). And do the same each time you go to use it. Don't leave your iron on for extended periods of time without re-tinning as it can cause the tip to go bad (stations that have auto off are a nice feature). And make sure to keep the tip clean, if you burn rubber or plastic, etc, solder won't want to stick & you'll need a new tip.

Sure there's lots of video's on youtube on proper technique. But tin your tip before you start, (& again every so often if your doing lots of soldering) as it helps to properly transfer heat from the tip to the parts. Depends on what your soldering but try to put the tip on both parts your trying to solder. Then feed the solder from the opposite side. This assures the parts are hot enough, the solder should flow easily, if not, the parts aren't hot enough. You should not have to feed the solder, touching the iron tip, as this will likely give you a bad/cold solder joint.