So one thing that I look forward to achieving in Halo 4 besides 130 SR and having fun, is completing 100% commendations, so I decided to share some of my thoughts and tips and see what you guys have to say too!
Weapons:
DMR/BR/LightRifle/Carbine: These are pretty easy to complete by just using them as your main weapon. Aim for the head.
Assault Rifle/Surpressor/Storm Rifle: Could be done by using them as your main weapon but what I found to be a great way to get kills with these automatic weapons is by using the “Firepower” Perk along with dexterity and using these weapons where appropriate (having these weapons as a secondary gives u the ability to have a DMR or something for mid far to far range)
Magnum: One word, Swat. Also, with dexterity(fast reload+wep swap) you can easily chase a weakened enemy around a corner(carefully!) and spray some pistol into them to finish your kill
Plasma Pistol: One phrase, OMFG. This seems like the hardest Weapon commendation and personally I have on set strategy yet to effectively get kills besides just saying a prayer for my K/D and trying to jump people and hope for the best. I’d love to hear if anyone else has had any success with this.
Boltshot: Pretty easy to get kills with. Charge up and use at close range.
Frag Grenades: Easily gotten by nading people.
Plasma Pistol: Sticking people, vehicles, pretty easy
Pulse Grenade: You only start with one of these and personally I have not fully gotten good at using these. KotH seems like a great playlist to go for these, just dont expect this one to be quick, and just try to learn how to use them properly
Shotgun: Easily gotten in Flood or a little more slowly through ordinance
Sniper: Got this done in team snipers, besides that multiple maps have starting sniper spawns and ordinance is always nice.
Rocket Launcher: BTB and ordinance. Exile is great because its easy to sprint and snag the rockets in the beginning(even b4 their ordinance icon pops up on your radar.)
Laser: Been doing this through ordinance. Pretty good to do in BTB
Sticky Detonator: Ordinance and just picking it up off of spawns. This one is pretty easy because it spawns on alot of the smaller maps (basically what youll be playing if your not in BTB.) I’d say this gun is a bit harder to use in BTB as well so your better off sticking to plain slayer if u wanna use ordinance and get this at the same time.
Railgun: Ordinance and pick up off of spawns…not really much else to this one. Its not too bad for taking out vehicles but unfortunately I feel it has really low ammo 
Saw: Spawns on Exile and is commonly gotten in ordinance. Basically use this as an assault rifle with 2x the firepower, very easy to get done.
Needler: these spawn alot on maps and are commonly gotten from crap ordinances. pretty easy to use, and you shouldnt have too much trouble with this one
Sword: Flood? - not 100% positive if it counts but im 90% it does. Besides that the sword spawns on Adrift and you can get in ordinance(probably will want to do this in Slayer and not BTB)
Hammer: Same as sword, basically except you can only get it in ordinance. Hopefully they will release a grifball playlist one day and this one will be quickly done in that.
Fuel Rod: Gotten through ordinance. Very good weapon, lots of ammo, be careful and go nuts in BTB.
Beam Rifle: Ordinance. Pretty fun weapon. Basically a convenent version of a sniper, go nuts and aim for the head.
Concussion Rifle: Ordinance…blow some people up. Easier to kill with this when you have a height advantage.
Incineration Cannon: Spawns on Solace(alot of the times I get it uncontested while everyone goes for the sniper. Gotten through ordinance as well. Pretty easy to get kills with, but I suggest using dexterity for the fast reloads as this weapon only has one bullet per reload.
Binary Rifle: Mostly gotten through ordinance although I’ve seen this spawn on exile alot and haven sometimes. One hit kill anywhere you hit someone. Don’t waste ammo on vehicles. Also be wary that there is a beam coming out of your gun that gives away your location. Imagine a red dot sight/lazer on the front that everyone can see(except ironically, you)
Scattershot: Spawns on a few maps, can be gotten through ordinance. This gun can shot really fast and is basically a shot gun
^^^^^^^I probably missed a few weapons, I’m gonna continue working on this thread until completion - adding tips and giving credit to any of your thoughts/tips!