Wall of text incoming, and i apologise in advance.
When sharpshooter, grab an Xbow and hunt down the patty. No point letting him heal or get the jump on you. Keep the pressure on him at all times. It's funny watching people wait for him to come to them. Get him on the run and you can win rather easily.
This also works for medic, although the lesser damage means it takes longer. It's kind of annoying seeing my bolts go straight into his head, only to do very little damage. For me headshots are either very luckily done, or when he's walking towards me.
Although Sharpshooter is an absolute god at owning the patriarch, i had at one time solo'd a 6man strength patriarch on hard with medic wielding an Xbow, on one of the awesome Skeleton's Bone Pile (SBP) servers. I believe i kited the patriarch around the [deserted base night] map and i felt a sense of accomplishment having pulled it off.
I digress.
Some tips:
Aim for the head whenever possible, even with shotguns. Firebug is exempt from this.
A close range shotgun blast to the head does significantly more damage due to the fact the majority of the shot is hitting the head. An AA12 set to full-auto spammed into a Scrake or Fleshpound in close range does more damage when using headshots than bodyshots.
A big help for Sharpshooters. The most effective and easily used combo for a competent player is 9mm, Handcannon and Crossbow. While i know a handful of players can use DHC effectively, i'm not one of them and DHC is absolutely worthless.
In my hands at least. xD
9mm is a good backup weapon when the HC is out of ammo either temporarily or permanently as it's damage and recoil make it viable to use. The HC packs enough punch to eliminate most foes without trouble and comes with enough ammo to be used as a main weapon. The Xbow isn't ideally used as your main weapon for everything and anything, but is best used to take out the things you can't remove with the HC quickly, or at all. Notice i gave no tips for the M14, so here's one.
Don't use it at all.
Commando is perfectly fine with full auto on everything. Using bursts to kill specimens with Bullpup or AK47, then switching to your SCAR that you kept in full auto just for scrakes and FPs.
A tip for removing Scrake infestations as commando: Empty your full-auto weapon of choice into the scrake, dropping it to half-health. Then pull out your auto SCAR and empty that into it's head. This will take roughly half a mag from each weapon, and given enough space can leave you unharmed or slightly injured. This isn't advisable on smaller maps in confined spaces.
Demo: Aim for the middle of groups, try to pull out your 9mm for single specs to conserve ammo.
Do not spam your GLs. This is wasteful and should only be used as a last resort. Remember that you have 11 grenades magically attached to your body, and that you don't have to rely on your M79/M32 all the time for everything.
Medic: Have you used the Xbow before? Do you know the trick to hitting lon range targets with it? Good. The MP7 works very similarly to the Xbow in that the projectile speed is subsonic, and takes a small amount of time to reach it's target. A good medic will have the MP7/Xbow combo to eliminate pretty much anything that everyone else can't/won't handle.
If you can, put yourself in front of the specs attacking your teammates, except for the Fleshpound. No point putting yourself in front of this one, he's already got a target in mind. Scrakes like to change targets a lot though
Berserker: I've got nothing for this one, except this. You're a berserker with a 9mm for a reason. You can kill crawlers with it if you don't feel confident to tease them.
Firebug: Today i saw someone spamming the FT and i thought: "he'll run out of ammo quickly playing like that" and guess what? He did run out of ammo. Now i, and other people floating around forums like myself say this: tap, tap tap the flamethrower, don't hold it down unless it's an emergency. I'm not an expert on this perk's use, so i'm probably not right about tapping it, ask for a second opinion on this one.
If you read this then gratz. You learnt something xD