Important to note that these days you really should use lead-free solder. You'll find all sorts of people going around claiming that leaded is better, but it's really not, and it's not worth the health risk. Your iron needs to be about 20c hotter than for leaded and your solder joints will look dull instead of shiny. If you find lead-free solder to not flow properly to be grainy your iron isn't hot enough.

Still wash your hands after using lead-free solder by the way. You don't want to be eating rosin or copper either.