I put my top tips here after about 15 years of collecting the best tips from hundreds of GMs:
https://slyflourish.com/top_advice.html
- Let the Story Unfold at the Table
- Set Up Situations and Let the Characters Navigate Them
- Be On the Characters Side
- Use Tools and Techniques that Help You Prepare to Improvise
- Focus on your Next Game
- Build Your World, Campaign, and Adventures from the Characters Outwards
- Pay Attention to Pacing
- Focus on the Fiction First and Mechanics Second