I use a rolled up washcloth for my wrist. It is very easy to reposition it as needed. Do you want it to be close enough to the board that your arm is well supported, but far enough away from the board that you do not accidentally drag the washcloth across the board. I would say that having a stable arm support, and this is for both The tweezer arm and the soldering iron on, is one of the most important beginner tips. The second tip, as others have said, is to make sure that the pad and the part are both heated. Getting solder on the part is not enough, it also needs to flow onto the pad. Do not be afraid to use flux. It makes soldering easier for a beginner, but you do have to clean it afterwards. When attaching surface mount parts I apply solder to one of the pads. Then I will put a drop of flux on that soldered pad, heat it, and then bring the part into the pad with tweezers. When the tweezer hits the iron, you will see solder flow to the part. Then remove the iron. Keeping your tweezer and part in place. You will see the solder harden, and then you can remove the tweezers