Need some tips on brewing higher quality green tea

Hi all, I’ve been enjoying authentic green teas for like 2 years now. I mainly bought a budget everyday green tea from Vietnam, and it’s quite simple to prepare, I just brew it for 3 minutes with 80C water (3.5-4g 200-250ml).

However I recently bought some nice Japanese green tea, and the brewing instruction is the following: 60-65C water and steep 4-6 times, for 10,10,20,30… seconds.

If I’m being honest I’m not really a fan of multiple steeps, I like to prepare the amount I will drink in one go, and I often have enough time for the single steep method due to work. I tried to brew these teas like the cheaper one, and also the multiple steeping method and I do it with like 50-60ml of water at a time and I just mix them together in a cup and drink it that way. But I get very mixed results, it either comes out tasteless or a bit too bitter at other times. These are expensive kinds of tea and I wanna make sure I prepare them like they should be prepared and don’t waste them.

Are there any golden rules on how to brew these higher quality teas in a simple way?