It is better to vary depending on the structure of the table,opponents, position and response moves.If it is easier for a beginner, then it is more difficult for a regular (they can exploit your bet sizing).
Knowing how much to bet is critical in poker, as a good bet makes you win important chips and not lose them. Let me give you some betting tips: If you think you have the best hand, make bets to get more chips, don't bet too high or you could lose precious chips. Another tip is: if you think you have the best hand at the moment, but can easily be beaten by a better hand, I advise you to make a reasonable bet, around 70% of the pot, as your opponent will have to pay the price if he want to see more cards, and you can win chips if you don't bet too high too
I like betting the same amount (in ratio to the pot) if beginning because it gives you less things to focus on and it disguises the hand strength if you bet the same with bluffs, draws, made hands and the nuts. Once you grow as a poker player, you'll probably find exploitative spots where you may want to bet/raise various amounts.
As for open-raising, same concept for me. I like picking an open raise size and sticking with it (adding 1 Big Blind per limper), but of course this doesn't mean I can't adapt later if I want to change strategies for exploiting opponent[s] or for effective stacks shifting.
You don't want to be open-raising for 3 bbs at an effective stack of 50+ bbs AND open-raising the same amount at 10 bb or less effective stacks. When short stacked, you may want to lower your raise size and all bets on future betting rounds or just open-shove All-in alternatively on hands you want to play.
I think Daniel Negreanu had a short video on this via YouTube; let me see if I can find it:
1st place finish at CardsChat 30 Day Course Freeroll (May 31, 2020). As my first ever CardsChat event, this one will always be special for me.