This doesn't really need a guide and there are loads of way to do it, but here are some tips.
- Knock out targets get out their car when attacked.
- Eliminate targets try to drive off.
- They wont leave their convoy route unless they spot you, making road blocks a great tactic to set up ambushes.
- It is impossible (I think) to get a police wanted level while taking on "criminals", so don't be shy with explosives and bullets.
NightmoonStalker has mentioned that you can be reported to the police, i believe this is only if the crowd respond to your actions quicker then the convoy but worth noting.
- The final mission for me was unlocked from hacking a random pedestrians phone, long after I had completed the other convoy missions. When profiling them it did say they had a Convoy mission, but I had to hack their text messages.
Here is a boring way to do it that I find make these a cake walk:
1. Get to the convoy path in any car and then follow it backwards till you are about 100-200m away.
2. Block the path and squat behind your car or nearby "obstacle" with a grenade launcher and await your friends.
3a. If you have to knock out the target(s) then grenade the first "support" car.
3b. If you have to eliminate the targets then aim to take out the target car first.
4. You then should only have a few people to kill. I would continue to use the grenade launcher if armoured dudes are angry with me or I'm enjoying myself. Otherwise, using focus and your gun of choice will work and try to stop any calls for reinforcements. Have fun!
5. If you still have to knock people out, then run at them as they usually only have a pistol, so man up!
...but don't die.
CrucialVelocity has pointed out that one of the convoys needs you to knock out a cop and you are better off rushing the target after initially attacking the convoy. You don't lose much reputation for attacking a cop but I found its easier to do this one quickly because police are limitless.
The target is in the passenger seat of the second car in this one so taking out the first car as normal and running down the passenger side of the convoy to knock out the target works well... i then made my escape in his car just to add insult.
The final convoy crosses a bridge with the entrance very close to the start of their path, even with a fast car you are unlikely to beat them to the bridge. You can take a different bridge on the right of the map and cut them off at the other end but as CrucialVelocity has pointed out, if you drive against oncoming traffic you can remain unseen and get ahead of them. This is a knock down target with lots of guards.