How to focus - really focus when shooting landscapes.
Use a tripod every time you have a chance. Failing that a rock or a tree.
Pay attention to the composition and the light. If the light makes everything look dull shoot something else, maybe just a detail that is more suggestive of the place and of the experience of being in it. Also if the light in the scene in front of you is fantastic , turn around and see what it is doing to things in other directions including above you.
Don't settle for always shooting at eye-level, get funky and get down or get it up higher. A change in perspective can make a world of difference.
A backpack, a belt bag, or a shoulder bag full of whatever gear you aren't using at the moment makes for a wonderful ballast bag for a tripod or as a ground pod. Getting the bag off your back gets you to stop being a human mule too. Tire, stiff muscles make for a tired, stiff mind.
Bring a close focusing lens.
Don't carry too much stuff - it gets in the way.
About composition: satisfy your eye and mind first, listen to the blah-blah-blah about the rules of composition later. No one sees quite the same way do. Respect that.
You aren't seeing deeply enough or carefully enough or imaginatively enough if you walk away feeling like you got everything.
Practice doesn't make perfect - practice makes better.
Get out earlier and stay up later. But get good sleep too.
Be prepared to initially hate almost everything you shot. Being able fairly judge your work takes time.
What is also true is that a really great shot will announce its presence immediately, sometimes even while you are shooting. Chimp (looking at the camera's on board preview screen) sparingly. Remember that it is officially called a preview screen - it isn't the real deal.
Physically focusing: If your camera has it, use Live view and it's magnify function in conjunction with an LCD covering loupe (I like the 3x Hoodman) to compose and focus with. Use manual focus. Unless all of that takes too long and Somethign amazing is happeninfg in front of you. In which case aperture priority exposure mode is great.
Bracketing exposures brackets your treatment of the subject matter. Use Exposure as a creative tool. Sometimes makign a scene scorchingly bright or your shadows really dark tells a better story than a technically accurate description of the place and people like stories.
If you do use autofocus and your cameras have the function, use the auto-focus micro-adjustment tool to make sure your camera bodies are tuned to your lenses.
As the man said: focus on what you feel is the most telling feature in the scene. If there are any books set in that locale, read 'em. It will help you develop a feel for the place.
Most importantly: stay loose and have fun; let yourself play.
I know you asked a technically based question but technique is just a tool for sharing your imagination.