For dupe (duplicant) skill trees, Francis John has a great tutorial, but as a general guide:

• You’ll want to specialise your dupes but not too much. It’s fine to mix skills a bit.
• It’s better to mix activities if they’re all performed outdoors (building, digging) or all indoors (cooking, farming).
• Worst hypothesis, use the skill scrubber, so don’t feel afraid to experiment.
• Don’t assign skill points just because they’re available. Consider morale.
• Doctoring is usually not useful. I simply pretend that it doesn’t exist.
• Decorating and cooking are useful, but one dupe with each task is enough. (Or one with both - decorating isn’t too frequent.)
• Almost everyone benefits from Improved Carrying I and II. Late game you’ll probably want to assign them Exosuit Training.
• Francis John’s video is old and the skill tree changed in the meantime, so take that into account.

If you meant instead the tech tree, a few tricks:

• The top is usually more important than the bottom. For example if unsure about researching food or decor, go with food, as it’s way up.
• Things requiring only basic research (blue) and advanced research (purple) are specially critical, but your dupes can survive quite a while without materials research (yellow) or interstellar research (orange).