Favourite performance tuning tricks?

Question

When you have a query or stored procedure that needs performance tuning, what are some of the first things you try?

Answer 1

1. I comment out one table at a time to see which tables/joins is causing the slowness. Based on that, I add the proper indexes to help performance.
2. Eliminate outer joins wherever possible.
3. Eliminate using DISTINCT in SELECT statement wherever possible.
4. Play with joins or use nested queries (ex. WHERE EXISTS) to see which performs better.