Hi!
Well it's really simple if you have adequate equipment.

First of all it is vital when soft soldering that you clean the surface that you are about to solder.
That means using sandpaper and sanding away all dirt and grime.
Using acetone prior to sanding is a good advise to get rid of the grease and grime.
Soft soldering is mostly done with an electrical soldering iron........I use a WELLER 50W soldering pen with iron-plated exchangable tips (professional type) which is 30 years old that hold a constant temperature.
Soldering irons (angled and straight) could be found at general-stores but these have often un-plated copper-tips and these are not to good to use..more than a few times because the tips oxidizes and get black from sot (you see... iron-plated tips don't oxidize or get "dirty" from flux in the solder).

If you are about to solder together two piano vires.... let's say two 3mm pianowires......making a landing gear...it is much better to wrap them togetter first with thin copperwire so that the surfaces are held tightly together...then adding flux ...and then solder.
The best solder/flux on the market is the Great Planes "Stay Brite solder" It comes complete with soft solder (ad says its 5 times stronger than ordinary soft solder....and I agree...it is superior to any soft solder I 've tried in 30 years) and a small bottle of flux.
This flux is so effective that you really don't have to clean the surface before you solder ...just drop on some flux and heat the area with the iron.......then hold the solder against the surface ...still heating it with the iron......and voila! Ready!
The brightest solder finish I've seen....and strongest (soft solder that is).

Regards!
Jan Karlsson
Sweden
http://hem.passagen.se/airracing