If you are referring to tricks and tips, here are some I know:
1. Always carry some sticky bombs with you. You can: a) eliminate targets in a car. b) You can loot a security van (green vehicle, shown in the map when spotted)
2. Drive on the rail tracks to evade police. They don't follow you there for very long.
3. Call 911 and ask for police help while in a gang fight on roads. They will kill the other gangsters, while you can steal the cop car and run away!
4. Call 'Downtown Cab Co.' if you need to go somewhere far from your current location. They will send a taxi for you.
5. another police evade technique is to go offroad. Police park there vehicles on roads and persue you running on legs, this will give you a chance to escape from their vision.