Check this video:
You'll get an idea about lag shooting.
And some of my duel tricks:
1. Run rapidly in a Zig-Zag way. This will help you not getting hurt.
2. Never run in a straight line, or in circles.It'll make your lag point easy to hit.
3. Never stop in duel , Always sprint.. Unless you use deagle or walkin weapons.
4. Check the opponents Ping , And shoot him accordingly.