Mission F1 - 120,000
For this one, all your really need to do is milk the time a bit so you have more time to rack up some points (preferably using the turrets for combos). Use the first three minute to slowly move to the two Tyrant Anti-air batteries and blow them up while you clear out every enemy you come across. You will then have another timer to clear out all of the remaining enemies - including any standing turrets and a tank - within two minutes.
Mission F2 - 120,000
You're rolling around in the most powerful vehicle in the game, so it's not hard to imagine how you get a combo going in this beast. Make sure you clear the whole area, as opposed to just going after the objectives, as there are a couple of vehicles in the right side of the map that can give you some extra points.
Mission F3 - 120,000
This is the usual defense mission, and I spent the duration sitting on the turret closest to where you start the mission. The relatively frequent spawning of Brutes should help you get the score easier than usual.
Mission F4 - 150,000
It should go without saying, but you'll probably want to do this before or after doing Vidmaster Challenge 2.0. You might also want to get a sniper rifle to help speed up the killing of the many Brutes and Elites on the level, and also keep the shotgun to quickly clear out crowds of drones. It may take a couple of attempts to get a solid combo/killstreak, but the big points you get from each enemy adds up fast.
Mission F5 - 120,000
Practice. I bought the auto sentry and the sniper rifle after some trial and error and that seemed to do the trick. One key thing to note is that you will want to get a solid multi-kill on the groups of grunts that spawn by kiting them around a bit until you get a decent sized group and then grenade them all.