Is returning to land more of a function of selecting the right fight to get into or more the skill of the pilot to win in more situations?
Both. In some ways, 'selecting the right fight' is more like a higher kind of situational awareness, one that is not limited to your immediate surroundings. It's kinda skill of it own, and an important one that is often quite neglected.
Do those with high kill to death ratios avoid things like furbals?
Some do, some don't. It's certainly more difficult do keep your K/D up when taking part in a furball vs hunting bombers or vulching airbases.
But K/D is very much overrated anyways. You can get a 'high' K/D by flying extremely cautious, but your score (as well as your reputation

) will suffer from your resulting very low k/h.
Do they avoid high ratios of reds to greens?
Again, some do, some don't. It's easier to survive with many greens around and few reds... but it's easier to get kills with more reds and less greens. It depends a lot on your skill level, the better you are, the less you benefit from a green horde.
Good players looking for kills do look for fat red darbars...
Do they always go in high?
Same answer - some do, some don't. Alt is life, but unless you are hunting for high alt bombers there is often no point in flying at excessive altitudes, you may be 'safer' but you also will see fewer kill opportunities.