Since there isn't a thread on this, I decided to create one that I could point to...
People think, 'Soldering. How difficult can that be?'
The answer is, 'As difficult as you want to make it...'
The fact is, there's a wrong way to solder, and that's the way most people instinctively try first.
You DON'T melt solder onto the soldering iron and try to get it to stick to the items you're trying to solder. This is GUARANTEED not to work. Why? Because the flux core of the solder will no longer be effective by the time you get the solder to the surface you are trying to solder.
You need a soldering iron and rosin-cored solder.
When you get the soldering iron, you turn it on for the first time, that's when you melt solder onto it. You turn it round and round and push the solder onto it and make sure that every part of the tip has a thin shiny coat of solder. This is called tinning. Ignore any drips that form and fall off. Then you wipe it on the wet sponge (you did wet the sponge?) on the solder station, or wipe it on a damp rag. Be careful if you use a rag, steam will form and if the rag is not thick enough (folded) you will get burnt. Wipe off all the drips of solder and any flux.
Everything you're trying to solder together must be clean. This means shiny clean. If it's copper, like perfboard, you need to polish it with emery paper (sandpaper) unless it is brand new. Boards may be tinned. They will remain solderable for quite some time and it is usually easy to break up any oxide film that appears on them. Components are treated to stay solderable for a while, but even they will not stay good for soldering for ever. A layer of oxide forms with exposure to air. YOU CANNOT SOLDER THROUGH IT. You may have to clean them with emery paper too. With resistors you fold the paper round the lead, hold it tight and pull it off the lead. Do this a couple of times to make sure the metal is exposed. Otherwise you can scrape the leads with a scalpel or craft knife blade. If you are unsure whether the part is clean you can check by pre-tinning it. Heat the LEAD with the iron, push the solder onto it, and check that the solder forms a thin film on it, just like the tip of the iron.
When you have inserted a component into the board, you push the tip of the soldering iron into contact with the lead AND the copper on the board. The tip must be tinned, but not dripping with solder. After a couple of seconds you push the solder (wire) into contact with the LEAD and the COPPER on the board. If you can get it to touch the tip simultaneously, so much the better. Make sure the solder flows onto the copper pad and the lead. If it forms a ball or puddle the joint is not wetted. The solder must wet the joint for it to be effective. You can see the instant when the solder collapses and goes from sitting on the surface to actually wetting the joint. You MUST be able to see that the solder slopes onto the parts and board gently and does not sit up like raindrops on a dry window. It should look like a little volcano with the lead sticking up out through the peak.
Remove the solder from the joint, remove the iron from the joint without disturbing the parts, blow gently on it if you like to cool it. Wait until you see that it has set or you will have to reapply the iron, because a joint that has been disturbed in the process of setting may fail.
Job done. Move on to the next joint.
Although many people swear by it, supplementary flux is unnecessary for the very large majority of jobs, and depending on it only encourages a poor technique.
Edited by wakibaki - 4/9/13 at 12:57pm