Just say no. The 1980's anti-drug slogan can be a power tool in your toolkit. High-performers are often rewarded with more work. Side projects. Extra-assignments. Special favors. It can be a great boost to your career and reputation as someone who gets the job done. It can also lead to stress, burnout, and resentment. Amplified across all facets of your life, not saying no can mean that others' priorities can supersede yours.
The risk is that everything else gets done...but leaves not time to get done what you need to live your best life - whether it's exercise, volunteering, getting more education or training, reading, or spending time with family.
Learning to say no can take practice. Give it a try. You don't have to apologize or explain. Just say no. And get on to what's important.