Soldering is one of those things that the more you do it the better you get.
My personal tip is clean the tip during use (damp sponge), a good hot iron with tip well covered in solder when going in to do the joint. Tin the wires well before soldering, hold wires with pliers.
What you don't want is a dry joint (where you don't have enough solder in the joint) this will be visable by being able to see the strands of the wires, what you want to see is a nice smooth finish on the joint.
Hope the above helps.
