Do get yourself a high wattage solding iron. 50W plus if you can. The higher the better to protect your cells from getting too hot. ALWAYS use a chisel tip soldering iron when doing your cells as you get more heat down quickly.
Rough up each end of the cells with sandpaper or a wire brush before you solder to aid in solder transfer. And do use a little flux to help.
Work on one cell at a time and let the cell next to it cool down before you move on. Lastly, don't forget to bend two bars for the ends of the battery if you're using deans! This helps greatly in attaching alligator leads.
if you are using deans, do the deans first. No one likes soldering LIVE battery leads!