Toad,
In HO and N its a breeze, however in larger S, O and G its allot tougher, the issue is enough heat to get a good joint requires a larger iron with higher wattage. I have been succesful using a good acid flux, this lowers the temp. required to solder the joint. However you must clean all the acid off of the work piece, otherwise it will begin to corrode your work. Are you soldering feed wires or joining track? This makes a big difference. If you are using any electrical connections use a Rosin type flux. Hope this helps.