Like henke said, func_detail everything that doesn't block vis as you map
"Skip" isn't really anything to do with optimization it's just a texture that we use so that we're not making extra cuts with our hints.
For hints (or any optimization task really), the best thing to do is do a compile of vbsp, load the resulting portal file and find areas where cutting visleaves would result in better vis calculations. I personally don't fully understand hints so I tend to use them sparingly but generally I guess you don't want a visleaf to straddle a huge area because then the calculation for that visleaf will cause the engine to be rendering way more because of that one visleaf.
Areaportals are very useful for interior spaces and
I'm sure they're very easy to understand so I'm not gonna go into more detail here.
Occluders are something you should definitely try not to use too much, they cull any model/prop from rendering that would usually be behind it. The best usage is probably on big flat walls that have tons of props rendering behind it which can't be optimized any other way.
Be warned that improper use of areaportals and/or occluders can result in negative effects (drastic fps drops).
When you get to the detailing phase of your map it can be useful to set fade distances for props as it will definitely help cut down on what's being rendered at any one time and can possibly negate the requirement for an occluder. Props are more expensive to draw while fading however so keep your fade distances short whilst trying to avoid nasty pop-ins.
Start small, work your way up as your map gets further along in development.
Another big tip I can give is to try and keep your map's boundaries small. Open space is nice, but too much of anything can be bad. That's where I went wrong with tanker, its huge open skyboxes caused horrendously long compile times.
Visclusters don't help with optimization and their primary use is to cut down on map compile times, however if you use them incorrectly you will mess up your map's vis and cause tons of issues, so it's best to take it slow and use them in conjunction with hints to get optimal compile times. In Tanker I used them to help shorten how long the vvis calculations of the large open areas was taking.
EDIT: One of the best things you can probably do is
download a decompiled version of an official map and analyse how they did their optimizations.