Hi there, the reason i am writing this solution is just giving you some tips and tricks about some missions that really pissed me off. (read every solution and comment before reading this, so it may confuse less.)
If you're stuck on having missions left with time limit and accuracy or headshots at the same time, don't do both together because the pressure is just too high to miss shots.
Pick a pistol or use the explosive Shotgun (code: 486-555-0100), also health and shield (code: 482-555-0100 or 362-555-0100) before you restart each mission for the maximum amount of headshots and accuracy.
The helicopters aren't really needed, but in case if you need to know it: it doesn't spawn every time, so you might have to restart the "Bang Bang" Mission a couple times before it shows up. (that's the only time i used it btw.)
Rocket Launchers aimed at vehicles gives you 0% accuracy. Had to learn that very painfully in the "Going Deep" Mission.
For the Mission "Momma's Boy" you have to win every round and after that you kill the guy who was betting against you. (which is suprisingly not canon.)
For the Quickdraw the RPG checkmark in "Kibbutz Number One" you need to activate auto aim and flick your RS into the direction where the RPG guy spawns after you killed enough people.
For the "Sexy Time" Mission, the Yacht has 4 Hitboxes, also using the
button goes into first person perspective and it helps to see where your shots are going. you can hold
Button together while trying to low yourself right above the water for easier aim against the boats.
For the "No. 3" Mission (followed close checkmark), don't crash your car at all and hit the ramp before brucie lands on the boat. (you'll probably have to play this mission alot to know dangerous areas.)
For the "Caught With Your Pants Down" Mission, if you fail 14 shots for the Sharpshooter checkmark, then you can shoot the pilot in the head so you can restart the mission much faster.
If you got the Truck landing checkmark in "Dropping In" you don't have to land perfectly on it again, just fly into the ground and get in the truck.
You have to skip the Cutscenes in "For The Man Who Has Everything" to make it in time. (i skip every cutscene in this game which might also help.)
In the mission "In The Crosshairs" you can climb up the Chimney in the video at 0:51 like mentioned in the comments in the following video, just don't hold or tap
, take your time since its easier to recreate the whole video.
Also if 4 Shots 4 Snipers doesn't work, getting arrested and retrying helps towards the checkmark.Solution for TBoGT: Gold Star in Grand Theft Auto IV
In the Mission "Ladies Half Price" you have to hold
to get rid of the guy holding on your boat quickly.
Also in the final Mission, you don't have to recreate the sniper shooting in the following video, but the flying parachute part was needed to make it legit under 10 Minutes, since it took me 30-40 seconds longer to finish the mission despite using shortcuts.
Hope those tips can help getting you a bit closer to the 80 and 100% achievements.