Make sure you have a decent soldering iron, then, lightly sand the tip, until it is shinny, heat up soldering iron, I use ( lead free tinning flux ) I dip the soldering tip into the tinning flux, then melt a dab of solder on tip ( I use silver bearing rosin core solder )
The solder on the tip helps disperse the heat transfer better, ( tin your wires ) dip wire in tinning flux, then hold soldering tip to wire ( with some solder on tip ) until wire absorbs the solder, then tin the mother board ( get a dab of solder to stick to the pad ( same way as above ) then hold wire to pad, and solder together, don't heat too much, but if you don't heat enough, solder will be clumpy, and won't bond well, should look like a smooth dome shape, almost shinny.
( might need to get a higher watt gun? )
At least a 25watt iron
I use a soldering station cost me $69 shipped has a built in heat gun, volt tester, soldering iron, and power center.
Search " 853d soldering station "
Free ship! Might be what you need?
Hope this helps
J Dot