Not all solders are equal. Some types, especially the lead-free take a lot higher temperature to flow properly. You might try 700 or 750 if you are using lead free. Also you didn't say if you are using rosin core or straight wire solder. Either way, a little flux on the connection before you join the parts is a good thing.

The best advice I can give is to get clamp to hold your wires and parts together. That way you can concentrate on getting a good joint instead of burning your fingers. Soldering is an art and takes a lot of practice!