Being a beginner, I haven't perfected soldering with cheap Chinese kits yet (I'm sure some get it right the first time and that I too should have by now, but it's never late to learn).
I haven't worked much with SMD yet at all, for good reason (if you check below to see the through hole issues).
The only exception are relatively large (the largest I could find cheap) SMD LEDs, which can be soldered to stripboards/veroboards relatively easily.
I might dare soldering one or two of those on a PCB with proper pads, but nothing else. Maybe in the distant future, when I also have found a good/cheap magnifying solution.
A few issues I've noticed so far:
1) IC rotation:
Sometimes it happens that I turn the IC the other way around, and/or possibly other issues (of course if the IC is the wrong way around, it's hard to tell about other components).
I believe it's mostly the IC, as the capacitors (plus polarity), resistors, etc. are all well marked, and I test every single component before placing it. But I don't always find the IC rotation obvious.
Once I resorted to seeing an image on the internet where the kit seems completed, and following that same rotation, which... might have been wrong.
I'm not sure how to address this point, but finding schematics on the internet (IC datasheet + kit schematics) and then using continuity check to find which contact on the PCB goes where might help prevent me repeating the mistake.
2) Dry solder or VIA contacts getting scraped off:
Sometimes I'm not happy with how the solder joints look, and try to add more or remove the dry looking solder.
Sometimes the contacts around the VIAs (if that's the right word) even come off during the process, but it seems to only happen on some boards.
On those same boards, it's very easy to remove solder mask (very light pressure will do it, even the soldering iron can free the copper - but maybe that's normal), which is also a good thing since it can be used to solder those pins that don't have good VIAs anymore.
Dry joints might be related to the solder used (as a contributor, not sole reason):
I recently changed solder. I had some German solder which worked really well (which was actually used up), and now I have two formulations of cheap solder from China. Supposedly 60/40 (larger diameter) and 63/37 (smaller diameter). Flux as written is either 1.5% on both or 2% on the first one (would have to check).
So, I might have to learn how to work with this solder. I can change the power on my soldering iron, but not an exact temperature. But there's always the human factor (melting it longer or shorter) which can influence the result even with no temperature control.
-- Testing PCBs
Once a PCB kit has been soldered, it might help to have a proper current limited power supply.
Lacking that, would you recommend using a series resistor?
Something like this:
The goal being to prevent short circuits and limit the current.
In some cases, hope is that it might even prevent a wrongly positioned IC or component burn out, but I'm not absolutely sure if it can.
The trouble would be getting the "right" resistance value for each circuit.
Using a potentiometer, it would be difficult to know the exact resistance value presently used (without measuring it after each adjustment).
In your experience, is this something to do or not to do? Obviously, without a resistor, the current is limited only to the power supply. Even with batteries, that can be a good amount. With most power plugs or even USB power banks, it can still be enough to cause damage.