A good place to connect the vacuum gauge is to "T" it into the line that goes to your power brake booster, or any other available connection that is direct to the intake manifold and not the carb. The only reason I say "not the carb" is you have to be aware which connection points are ported vacuum and which ones are non-ported vacuum (you want to use a non-ported source for this), and its just easier to use a direct to the manifold connection. If you have to use a carb connection, make sure the engine is a running at a very slow idle, hook a hose to the port you want to test, and feel it with your finger. If you feel vacuum (engine at a low idle) it's a non-ported source and ok to use.
I'd start by turning both the screws in until they bottom, then back them both out a precise full 3 turns. This setting will probably be too rich and that's ok. You want to SLOWLY sneak up on the setting coming from the 'rich' side. It can take a few seconds for the engine to respond to the change, so make your changes slowly and evenly (same amount on both sides at the same time).