first off, i suggest you read this post:
http://www.unknownworlds.com/forums/in...hl=melee+combatits not skulk-specific but rather is based on melee combat.
My tips/general overview of Skulk-Fu:
the skulk is built for speed and quick kills, and is obviously very weak in the defense department.
what you want to do as a skulk is NEVER stand still, NEVER walk in a straight line, and NEVER rely on the floor completely. these basics will help keep you from getting shot, which is the first step to killing

the problem facing all melee units is closing the distance between you and your target.
If you turn a corner and see a marine down a hallway, you can:
a) charge straight at him, which is what the marine expects, and you will die
b) hold forward, jump and strafe left or right to touch the wall, climb the wall and/or cieling as you 'spiral' your way towards him, making it VERY difficult for him to hit you. when you are close enough you make him your meal

aside from speed, another one of a skulk's biggest advantages is SURPRISE. in almost any game, if you surprise your opponent you get a huge advantage. Hide on cielings, above doorways, ANY place where you are out of sight, and hold still. looking around turns the skulk model, (which is pretty long) making it easier for them to see you. Try to attack enemies from ABOVE or from BEHIND and you are almost guaranteed a kill

<--- if possible, this is the situation you want
Knowing the map very well can help you find good ambush points.
Next is Parasite. This little bug works wonders. Fire it at a marine who is too far away for you to get to without dying, and retreat. Draw him out. If he comes to you, he's done your most difficult objective (once again, closing the distance) FOR you.
If you are ever in a place where the walls and cieling are very jagged or have lots of things sticking out of em and you absolutely MUST use the floor, JUMP like a bunny on crack. JUMP from side to side and bounce around as much as possible. Remember it is mind-numbingly easy for a marine to shoot a skulk traveling a straight line.
Use hivesight. If you see a friendly about to attack a yellow blob, wait a split second (if you are closer than he is to the target, i.e. you are in a vent), or charge straight in (if he is closer). It's hard enough to hit one skulk, but if the marines have TWO skulks to aim at, you haven't just doubled your chances of winning the skirmish, you've probably squared them.
That brings me to the next point - skulks are SKIRMISHERS, that is, they are built for small battles, not assaulting bases. They can take down small outposts by either:
a) finding a blind spot on a turret factory (turrets cannot shoot thru the TF) and chomping on the factory there to bring down the turrets, or
b) finding a place where only ONE turret will shoot at you, and kill it.
Killing turrets involves holding down your attack button while circling the turret. It takes some bravery the first few tries, but you will quickly learn that
turrets turn slower than you can circle them. After 13 bites the turret will go down.
Advanced stuff:
Leap - this thing makes a skulk about 20 times more deadly to a marine

As you should know by now, closing the distance is the only thing that can keep you from killing. This gem of an attack sends you hurtling thru the air straight at your target, effectively covering your distance in under a second.
You can use leap to "fly" by leaping again in mid-leap. Leap is also GREAT for hard to reach places, and for surprising the hell out of a marine. In places with tall ceilings, such as the Cargo Bay on ns_nancy or most anywhere in ns_hera, instead of leaping
at a marine, you can leap at the ceiling
above him, then drop down on him from behind in a split second. It's
extremely disorienting for the marine and even if he does see you leap, he's not expecting you to go straight up, making it super-hard for him to hit you. An easy kill

The most simple use of leap is to leap straight at the target, and while in air switch to Bite, to deliver upon contact with the marine's face

Xenocide - You won't often get the chance to use this awesome ability, but when you do, make good use of it. This attack turns you into a giant BOMB - any marines in the blast will become red wallpaper instantly

I highly recommend you run towards where you want to explode, press Xeno (it has ~1 second arming delay), then
quickly select leap and leap straight at your target. Splat. You can take out clumps of unarmored marines with this.
Upgrades and combos:
Carapace - great upgrade for skulks, always. Those extra armor points can EASILY mean the difference between life and death.
Regeneration - only useful if you're camping a vent, parasiting people, taking a hit, and retreating. In normal combat, if the marines are worth their salt you will not have much of a chance to use this; you'll be dead. My recommendation is with Carapace.
Redemption - Like regeneration, except it doesn't always work and COMPLETELY displaces you from what you were doing, no matter how important it was. I really dislike this upgrade, but its up to you.
Adrenaline - Not very useful for the athletic skulk. Only leap and parasite place a considerable drain on your adrenaline, and those are not things that you need to use in rapid succession.
Celerity - my favorite upgrade for the skulk. Makes closing distance a cinch, lets you practically fly across the walls and ceilings onto unsuspecting prey. In close combat it makes your opponents wince at the fact you aren't in their sights for more than a tenth of a second. Especially nasty with Xenocide
Silence - good for stalking people, especially in combo with parasite and liberal use of Chuckle

It does NOT, i repeat, does NOT mute your attack sounds, it has been changed since the manual's publishing. If you're the kind that likes to surprise your enemies and kill them quickly without insinuating fear, this is your best choice.
Cloaking - sadistic at level 3, almost useless at lesser levels. Cloak in a commonly traveled area and eat people from behind. Get creative with this you can do almost anything with it. Note that when you are cloaked, you can make tiny movements or single attacks without decloaking. Wait 2-3 seconds in between each step or each attack and you will stay cloaked.
Enhanced sight - i don't really use this much. IMO its useless - if you can't see the enemies, turn up your gamma a bit

Scent of Fear - moderately useful, depends on the situation. makes hunting down endgame hiding marines a lot easier
Stick with cloaking

Late game skulk duties:
-Since you have minimal chance of killing HA/HMG marines, parasite them. Parasite every single one and make sure your teammates know what they are doing, where they are headed, everything. Intelligence is vital to victory.
-Stopping grenadier troops. While all other kharaa run away from troops with 'nade launchers, you should be running
towards them. A grenade launcher is useless against a skulk point blank, and you can probably rip him apart, even in heavy armor, faster then he can switch to pistol/welder and kill the guy who already has him halfway down his throat. Make sure you know the rhythm of grenade explosions before you do this, and dont walk on the floor in the off chance you will step on a grenade.
-Softening heavy armor. When the HA/HMGs are battling it out with the fades, lerks, and other critters, you should be in there, biting the rear ends of the heavies who are busy shooting the other direction. This can
easily swing the tide of the battle into your favor. Since heavy armors tend to travel in packs, Xenocide can weaken a group of them down the point where 3 acid rockets could kill the whole group

If you're going after heavies specifically with Xeno, try going scent/celerity/carapace if you have the spare resources and NEED to perform this costly action

Hope i helped!
have fun chomping away!