Well, I'll give you some tips.
1) If you're in LS, collect the AK-47' few times (you can find it behind the 24-7 store in Vinewood or in the Vinewood studio near that big mansion with a tennis court.
2) Use the HPV-1000 since it's lightweight and comfortable because of the fact that it's a bike.
3) Ride around the sorroundings of Glen Park and Willowfield since there's a bribe in Glen Park, a bribe in Ganton, two bribes in Las Colinas and a bribe in ELS.
4) Get a drive-by'eable weapon incase you need it.
Otherwise steal a Hunter or get a Rhino or you can snipe the suspects finding the sniper rifle in InterGlobal Films Studio located infront of that big mansion with a tennis court, collect it a few times since it will give you 10 rounds per pickup, aim carefully at the suspect car since it's fast, take a little time so you wont attract the police attention so fast.