A small amount of liquid flux is adequate, and I mean barely more than a slight trace of flux, because a drop is way too much, and will prevent good visibility.

I generally use a toothpick with a little liquid flux on it, but much of it wiped onto a scrap of paper to leave just a thin coat of flux on the toothpick, then dragging the toothpick along one side of the IC, followed by a close inspection to see that a tiny amount of the flux is on each pin or pad, and then proceed to apply flux to the other sides of the IC.

I can’t work on items that small anymore without magnification and very good lighting, and wouldn’t attempt it without a good magnifier lamp, even with great eyesight.

Just touching a clean, hot soldering iron tip on the connection is normally all that’s required for complete reflow of the existing solder. If there is excess solder on the iron’s tip, it will likely cause problems.

With enough magnification, it’s easy to determine if the proper reflow has been accomplished. If any of the connections appear to have too little solder for a reliable connection under close inspection, then it may require the application of a very slight amount of solder.

Adding the solder can be tricky, but remember that it’s probably going to be easier to add too much, than it will be to remove the excess, so just wet the iron’s tip enough to get a little solder to transfer to the connection. The liquid flux will insure that transfer takes place.

I would use ordinary flux core 60/40 solder on the iron’s tip, or a very small amount of paste solder, of the type intended for surface mount components applied to the pads (only if needed though).

source: Electrondepot.com

In this tutorial, we learn how to solder with a soldering iron. You will need: tinning pads, de-soldering braid, and an adding component. Start off by heating the copper, before you add the wire. You need for the acid to flow from the core onto the copper to create a surface that will accept the solder. A cold solder will break or cause burn. If you use too much solder, use the braid to remove it. Next, place the wires onto the holes and heat them onto the circuits where you want them to be placed. You may have to add some more solder to the iron if needed. Go slow with this and make sure not to damage the top of the board.

source: Wonder How To

source: http://wes51.net/dgctv-how-they-make-a-soldering-welder-station-k852d/