1. As US and Chimera build your refinery (ref.) as close to the oil tower so that the crusher/carrier can simple rotate around the building.
2. When you build your ref. you can already order the next building by holding the shift-button.
3. For US and Chimera you need 3 crusher/carrier. For Cartel the optimum number of k-max is 2.
4. It is sometimes usefull to use the "Q" key to move ur units from A to B (they will stop when they hit an enemy unit)
U should use it for ur scorpio attacks or if u move ur jevs to a building far away (f.e.).
5. You should never go for all oil nodes before you push out some units. Find a GOOD BALANCE between ECO and building an ARMY.

1. Fast Humvee attak
This a favorit opener to harass your enemy a liitle bit and to hinder him building up his eco.
Ref.> Field Generator>Light vehicle bay> 1-3 HUMVEEs

With that Humvee´s you can attak enemies refs. or/and shredder/kodiak/skycrane.
But take care, if it fails you fall behind in economy (eco). Next step would be taking your bank or you go for the next ref.

2. Combination Humvee + Javelins
Not that fast harass like No.1 but the combination Inf.+Humv will bring more options to you (and hopefully more damage to your enemy)
Ref.> Barracks [6 Marine´s for your bank]> 2nd Ref.> Field Generator>Light vehicle bay

Now you can attak enemies refs. with Humvee+Javelins or try to capture the buildings with yout marines. It takes about 4 Min. to have 10 Humv + soldier.

3. Combination ACCE + Soldier
Ref.> Barracks > 2nd Ref.> Field Generator>Light vehicle bay>ACCE + Javelins/Marines
Same as with Humvee´s, but the ACCE has more Hitpoints (HP) and could survive longer ^^.
It takes about 5 min. to have 8 ACCE + Soldier.

4. Guardians
Ref.> Barracks [6 Marine´s for your bank]> 2nd + 3rd ref. [Javelins defend your base]> Defcon 2>Field Generator>Helipad>Armory [NLOS+ countermeasures]> You have 4 guardians + 1 little bird in about 7:20 min.
Next step: logistical center > Hercules + Osprey (from Helipad)
With that your guardians be healed while they attak.

In my eyes Cartel is the most sneaky army. You should avoid to build a blob of tanks and throw them into enemies base.

You should rather harass with one or maybe two scorpio, jackal or a superhind full of vipers.

Im Mid-Game stealth helis are good to harass f.e. enemies refs. Keep in mind against what faction you are playing. U.S. normaly has a lack of stealth detection, so you should use it.

Here are the openers:

1. Scorpio
Scorpio is the most widespread opener for cartel. The tank is fast and can shoot farther than Puma or Humvees from the other factions. But you must keep your Scorpio in distance cause he is very weak (use "Q" key). Scorpio´s can smoke turrets for example to destroy the building next to it (ref. f.e.) or to capture banks with your soldier.

a) Ref.> Barracks> Vehicle bay = 1 Scorpio in about 2 Min.
b) Ref.> Barracks> 2nd Ref.>Vehicle bay = 1 Scorpio in about 3 Min.

You have to evaluate if you go on fast scorpio or take care of your eco.

2. Superhinds
Ref.> 2nd Ref.>Barracks > 2nd Barracks [tandem charges] >2x Vehicle bay> VIPERs+Constructor+Superhinds

In 6 mins. you have a sufficient number of units.

3. Light tank combination
Ref.> Barracks> 2nd ref.>Vehicle bay [4 Scorpios]>3rd ref. >[Prison module in barracks]> [3xJackal+VIPER in it]>[tandem charges]> Attak in about 6 mins.

Chimera has the best inf. at the beginning (Felins + SAS Sniper right from the beginning on), so u should use it. On the other hand u cannot build defense next to ur refs., so a good start is, to take the banks BEFORE u build ur 2nd ref.
U can use Namers or (Pumas with upgrade) to transport them from A to B. Namers can heal them (with upgrade) and/or u build a prison and use the prison heal. Felins can clear all banks if u do it like this. U can even try to take the bank close to your enemies start point. It is hart to counter it.
But if u ask yourself, how to counter it, maybe i can give u a recommendation.
Well, with Chimera u could build a turret in the area next to ur bank (on some maps) and with US u could build Humvees and Jevs. to attak the Namer(s) on their way to your bank (Jevs. kill Namer and Humv. the Felins/SAS).
If you survive this, the next attack is mostly by tigres. This is really hard to counter.
As Chimera you can build exosoldier (with upgrade). As US u can build blazer (with upgrade) or Raptors. But Raptors cost much, so I prefer to build more blazers than tigres that attack.
A better counter is to harass the chimera Player BEFORE he gets his mass of tigres. He needs at least 7 min. to build them. In this time his base is wide open. So harass him with an opener like Humv/ACCE + Inf.

So, let´s have a look at some possible opener for this faction:
1) PUMA
a) Ref.> SPEAR vehicle bay> [1 PUMA]
With that Puma you can scout and attak enemies refs. or/and shredder/kodiak/skycrane.
Next step: barracks > 2nd&3rd ref.> [Passengers accommodations in vehicle bay]>[more PUMA + SAS + Felin]
Sometimes i build a 2nd vehicle bay, sometimes 2nd barrack. One Puma alone is very weak but he is very cheap, you can build them fast and when you reach a number of >10 or if you combine them with SAS/Felin they are a a serious Opponent in the early part of the game.
b) SPEAR vehicle bay> > [2 PUMA in 1 Min.] > …ref etc.
c) Ref.>Barracks>2nd & 3rd ref. > SPEAR vehicle bay> [10 Puma in about 6 mins]

2) Namer:
Ref.> Barracks [5 Felin + 1 SAS]>Support bay> [Namer]>[attak: clear enemies bank first]> [Medical namer upgrade while you are going]
Push by building more Namers+SAS with upgrade and try to capture enemies buildings with your felins.

3) Neutron Bombers
It is not really an opener but i like to use neutron bombers in early/midgame to surprise the enemy a bit. Keep in mind that they are stealh bombers, so the enemy need stealth detection to see them coming.
U need SHIELD Protocol (most of the time u prefer to use SWORD protocol first) and then u build 1-2 airfields. U build 7 Neutron Bombers with upgrade and 1 scout jet.
7 Neutron bombers can kill enemiies HQ, 3 Bomber kill 1 ref.