how hard can it be to soldier and assemble Sanguinololu 1.3a without prior experience
Soldering really isn't that hard, If you practice first, then you can be reasonably confident of doing a good job. If you're buying a 3D printer, then you must be fairly technically minded.

Rule 1: Solder flows onto hot metal. It is practically repulsed from cool metal. To make a good solder joint, you must make sure the pin of the component and the pad on the PCB are hot.

That's pretty much all the rules. It's all about the heat. Most of the soldering problems I see are have something to do with heat transfer. Now follows advice about following rule 1.

Advice 1: Make sure the soldering iron tip is shiny. Shiny metal conducts heat well. Dull brown coating on the tip is a surprisingly effective insulator. Use tip cleaner. Touch the solder onto the iron. It should melt instantly.

Advice 2: Touch the iron to the pin and pad at the same time. Get them both hot, otherwise the solder will flow onto one of them and avoid the other. Do not blob some solder onto the iron then try to wipe it onto the pin and pad. As Olin mentioned in the comment below, you should touch a little solder onto the iron and use that to conduct heat effectively onto the pin and pad. Then apply the solder to the pad.



Advice 3: The way to be sure that the pin and pad are hot enough is to touch the solder onto them. It should melt immediately and flow beautifully onto the pin and pad.

Advice 4: Lastly, if the solder is being annoying, behaving more like custard, it probably means all the flux inside it has evaporated. Wipe it off with the iron, wipe the iron clean and try again.

Buy some vero board (strip board) and some cheap components to practice on. Once you're confident about making beautiful hot joints (you should be able to make about one every 2 seconds) you're good to go.