Level vigor. You level your weapon first, your character second (when in doubt: smithing stones over runes). Roll into or past enemies, not backwards in a straight line. If you die multiple times to the same enemy/group of enemies go back and take your time to grind and level with a group of enemies you can best more often than not. When you catch yourself running away from mobs regularly, you are probably under leveled. Talk to everyone multiple times (this one didn’t came naturally for me and literally wrecked the fun I had during my first run).

Specific Elden Ring tips I have given other first timers: Avoid Caelid for as long as possible (easily until after Liurnia and House Caria). Go to the weeping peninsula first, before fighting Margit.