In short, my play-strategy is:
I never open my hand, and I try to form simple combinations (and surely not "seven pairs and thirteen orphans, etc" ones) based on the most-likely possibilities that I see;
I remove all lonely dragons and winds first, so that more numbered tiles could gather;
I try to get one pair as early as possible, and stick to it – don't use it in triplets or sequences no matter what;
The harder a pair is to develop into something else, the better – if there are 2 winds or 2 dragons, I will stop using them as a pair only if I get the third wind or dragon;
If there is no pair of dragons or winds, I'll use 1 or 9 as a pair – and if I can't, I will use any other tile that formed a pair until I get a better option;
Once I get the one pair I need, I get rid of any other pair as soon as it formed, unless it turned into a triplet.
Ideally, I try to make it so the tiles are placed like "1-3-5-7-9", or as another version of this, to make it easier for me to form sequences as I can't reliably hope for triplets – so, the tiles that are too far away from one another compared to others get thrown away.
I start focusing on pure defence instead of forming a hand if:
Some player called Riichi (even when I myself got Riichi right after them)
Some player opened their hand 3 times
I am 2 or more tiles away from calling Riichi even though I had already discarded 15 tiles (12 tiles in 3-player mahjong).
I defend myself by choosing either what the Riichi-player or other players just discarded, or by discarding the tiles others discarded/used the most during the whole game.
Is there anything wrong with my strategy?