To achieve a higher ranking in PUBG Mobile you will have to spend more time playing, at least 2 hours a day. Drop last from the plane or drop to places with fewer houses to loot them since there is a high chance nobody will land there and of course avoid the hotspots. For killing try to find bots since they are not threatening like a real player. Try your best to survive until the last white zone and achieve victory. This is a pretty boring way to play but it is the most proven road to the top ranks.