First 2 lessons in hold'em are ...
1) Learn how to calculate stacks. Do not measure our stack in chips. Measure it in big blinds. Divide our chips by the big blind. If we have 2000 chips and the big blind is 20, we have 100bb. Measure everyone's stacks this way and always recalculate our stack when the blinds raise or whenever we win or lose a significant pot.
2) Learn table position. Always be aware of our seat at the table and we should be playing at least half of our
hands from the cut off and the button, the last 2 seats. Post- flop we have advantage acting last (in position) so we want to be in position as much as possible.
Once these 2 things are understood, then we can move on to pre-flop play. This involves pre-flop ranges and learn how to open and defend and even 3-bet and all of the sizings that go with that.
Post-flop tactics become a terrible mess in a hurry if the pre-flop is not played properly, so learn stacks, how to measure them, how to define deep, medium and short stacks, then position and to be in position as much as possible, then learn pre-flop play. Once all of that is done, we can take the training wheels off the bike and move on to all of the post -flop stuff.