A few rules to follow to unsuck yourself as a commander:
#1. Don't touch those friggin turrets until mid-game.
I know it may look tempting (OMFG, THEY SHOOT BY THEMSELVES!), but turrets are horrible beginning static defence unless you really put alot down, which you don't want to do, as it cripples your res so you can't do anything.
#2. I don't want to see a friggin turret factory in marine base
If you want electrification, then build a turretfactory next to a res node (preferably an important one). then electrify either the tf or res node. The electrify will protect both, and if the res node is an important one (temperature control, mess hall, south loop, etc.) Then you have the option of electing both, or putting turrets down to lock down the choke. let the tf rot in ms isn't going to get you anywhere.
#3, Mines, mines, mines.
Without those turrets, mines are great at killing skulks. When placed effectively, they do a much better job than turrets. 1 pack won't cover a base, though, you'll need minimum 2. And ffs, replace them if they explode. Mines also are useful around small outposts to keep the pesky skulks off while you're rushing that hive.
#4. Warning: May or May not screw the game for you.
Electrify is a very powerful defensive measure, however it'll blow a hole in your wallet the size of my penis (In reality, that would be a small hole, but on the internet, anything is possible!). 30 res can get you: w2,a2, mt + 5res, 2 pg, upgraded armory, etc. Many of those things are much mnore useful than an electrified rt. But i'm not saying don't electrify. Use in moderation.
#5. Rush crucial upgrades.
Your marines arn't going to kill Holy_Devil out there with your puny level 1 lmg, and lvl 0 armor. w1 and a1 is a MUST in the beginning, some comms like mt in the beginning too. All three of these upgrades can mean the difference between "OMG GUYS YOU SUCK, IT WAS JUST 1 SKULK" and "NSPlayer (LMG) Holy_Devil". And if you can't make a decision on where to spend res, always spend on upgrades. Electrifying that node is no where near as useful as w2. Also, keep the upgrades coming, even if you're a bit short on res. If you don't keep up with the times, your upgrades will not be able to catch up with what the marines are going up against, and sooner or later, you're going to have two fades on your marines and you only have a1. You should have atleast a1-w2 by the time you see a fade, then shotguns will shread them to peices.
#6. Don't be arrogant.
You're the comm, not king of the map. Don't ignore your marines they offer good suggestions. If you respect your marines your marines will respect you. But then, don't let the marines push you around. You're not king of the map, but you're still the comm, and you're running this joint. Ignore Isamil screaming for a shotgun, and get a phasegate to devicenull in Sewer instead. Find the balance between the two, and you won't lose.
#7. Use that res!
Unless you're saving for a mass equipment suit-up for your marines, you should never have more than 40 res (the most expensive would be w3, a3, or protolab). If its sitting there, its not res, its garbage. Res ins't truely res until you use it.
#8. PHASE DAMNIT PHASE!
Phase gates are extremely crucial to winning. If you can't get there and reenfrorce your marines, then you've already lost.
#9 The observatory
This is one of the more useful tools that you'll be using the most. Ping areas where you hear some action going, gather intelligence, and that way you can make the best move. Marines getting slaughtered? bacon them back to base..no sense letting them die.
#10 WTF are you doing comm?!
Keep your marines informed! Don't just sit there quietly twiddling your thumbs. They have a hive going up in Eclipse? Tell them! Getting armor 2? Report it! You want them to get to that res node? Don't jsut give them a waypoint! Tell them exactly what you want, and exactly what you're doing, and exactly what you're planning to do. This will get thier priorities straight. This can mean the difference between "God damnit, don't knife that res node, i want a phase gate there...crap here comes the onos." and "Phase up, heavy train away!"
#11 "Okay, someone else comm now"
Never EVER get in the commchair unless you're planning to weld it shut with you inside. There are many people who think they're good marines when no one wants to comm by jumping in the chair, putting down two ips, an armory and a tf. THEN they get out, and say those terrifying words "Okay, who wants to comm?". Not every comm will go for your basic load out base. Heck i don't ever get a tf until later in the game. Some maps just scream "relocate!", and if you put even one building down, relocation is already dead: You've wasted res, you've wasted time, you've wasted the time of the marines who are currently buliding the structure. You get in the chair, you stay there.
#12 "Holy crap! i need a medpack!....comm?"
a VERY common mistake that happens often is that you have a skulk in base chomping down on your armory. Comm jumps out, gets killed, and now the skulk is free to camp the ips. NEVER jump out of the chair to kill something as a light marine. If you've got the res, drop yourself some equipment: heavy armor, hmg, or jetpack (if you get into the chair with a jetpack, the fuel tank starts empty when you jump out, so this isn't reccomended). As bad as it might look, if your team does not have someone in the chair, they can do absolutely nothing. Stay put in the chair, scream for someone to get to base, anything but get out of the chair unless you're toting some heavy-duty equipment.
#13 Commander: NSPlayer
NOTHING scares a marine more than NSPlayer in the chair. the LEAST you can do is change your name.
[Edit1] For accuracy of turrets [/Edit1]
[Edit2] added #11 - #13 [/edit2]