Here are some strats and I hope, at least some of them would be useful. All videos on Russian, but, if needed, i could translate them.
"Аренда" - could save couple of seconds
The route for the 2nd half of the novice section
An easy (IMHO) way to steal in the mall
Dealers with guns in the hood - safe way
And killing Code E in Headhunters headquarters. Easy and fast (weird breathing noises, sorry)
Update on weapons strat at the start of the game. Distance between Tre and the camera makes a huge difference on the spawn of the enemies and NPCs. So, if this distance is minimal, the area in front of Headhunters' headquarters would be more crowded => better chance to find the guy with shotgun or uzi. I did some tests, and the difference is huge. This camera gives like 40-50% chance to find the needed weapon, and this is a lot better, than was before, and makes grinding for a good start less painful.
Update on a 2nd mission in the game (Landlord in Beverly Hills) When you should damage his car, you can leave it to Derril. Go to the office and start destroying things. After the cutscene with a broken car, you would be in front of the office. Walk inside and leave graffiti (if you did enough damage already). This is not huge but can save a couple of seconds.
New strat: After robbing the bank, go to gangland, to the striptease club (you have 2nd wanted level) => buy 3rd alcohol drink two times => Kill the bartender (You will need 3 hits, and all this should be done before 10 cops would be after you on 2nd wanted level) => After the kill you get 3rd wanted level and SWAT squad will be after you. They should have pistols, shotguns, and carbines. Kill headhunters, use your pistol to kill SWAT and take their weapons, then use it to take red-light district and underground or keep a weapon for the mission after fights in the Grand Central. You can use the weapon in headhunters headquarters to scare enemies and leave graffiti too. This is still work in progress, a bit risky (if you die, you lose 2-3 minutes -_-) and RNG heavy strat but I think it's worth it (most of the time). I will try it in runs and make sure.
