Here's a few threads that should help.
Soldering to 'pot' casings
More on soldering to pots
Soldering tips & tricks
I never blow on solder joints because the outside can cool quicker than the inside causing problems similar to a 'cold solder joint' which is a solder connection where one or more points being soldered are not heated up fully.
Solder flows into and sticks to a clean surface (free of oil and contaminates) that's been properly heated.
You need the heat to transfer from your tip, into the solder then to each point that is being connected till the solder flows onto the components.
Flux helps heat transfer and solder flow.
If your solder doesn't transfer off your tip onto the component then the component hasn't been heated enough.
The trick is to get on, heat it quickly and fully, then get off (sounds kinky I know )
One thing I've found, especially on SMD components, is that if too much flux is used and not cleaned off properly it can make a sticky surface that dust particles stick to. Sometimes dust particles contain conductive material and can short a line.