Star Wars: Battlefront II/Underground Ambush

Assault the Lookout Command Post
How many steps can they break this into? All you have to do for this objective is get within range of the Lookout CP, marked by the yellow arrows.

Capture the Lookout Command Post
You should have no problem at all with this objective; there will be maybe 2units at the top of the structure when you get there. Dispose of them and capture the CP.

Capture the Highway Command Post
This is where it starts to get tricky. Move down the "highway" with your units, paying attention to any mines that may be set the road (try using the elevated sidewalk to the left to avoid them). Methodically eliminate any enemy units that try to stop you, and don't ignore any of them. When you get close to the CP, CIS forces will try to stop you with AATs. The best way to survive against these is to position yourself so that there is a friendly AT-RT between you and the AAT (try not to pilot one yourself—it's easy to get killed, and you won't be able to capture the CP while on it). When the CP is taken, the tanks will disappear.

Secure Hangar 10
First, spawn as Obi-Wan Kenobi and remove any enemies around the CP you just captured, then move in to the hangar area. After clearing out any droid close enough to interfere with capturing, just stand next to the CP and press the "Force block" button ("F" key on the default PC controls). This will block all enemy fire from the front and sides. Work hard to keep Kenobi alive through this objective; he'll come in handy later.

Fight General Grievous
Welcome to the world of Hero Battles in Battlefront! This is your first fight against another hero, so you might need detailed instructions. The first and most important rule in hero battles is: Know where your target is at all times. Because Grievous' attacks are so much more powerful than those of an ordinary unit (and even compared to other Heroes), you have less room for error.

The second rule: Know your target. Know your character's strengths and weaknesses, and know theirs. Use these facts to your advantage. In this case, you have two distinct advantages: you have a ranged attack (lightsaber throw), and you have the ability to "fly". Grievous has no Force-related abilities, meaning he can't Force jump or throw his lightsabers, so he must get close to you in order to hurt you. Therefore, your safest method of attack is through your secondary attacks.

Throw your lightsaber to damage him when he is not blocking. When he is blocking, you have no choice but to attack him up close. When doing this, start from several meters back, and sprint toward him. When you get close, press "attack" 3 or 4 times, and your character will unleash a deadly stream of attacks at Grievous (Obi-Wan Kenobi has one of the most powerful "sprint attacks" in the game). As soon as you regain control of where you're going, you should force-jump away, because Grievous will retaliate... and his attacks are more powerful than yours. Just continue this until he is defeated. If you run low on health, run away and kill some droids (they spawn behind the support beams, near the end of the map—just look near the Hangar CP).

If Kenobi is killed, respawn as either a Jet Trooper or an Assault Trooper. Unload your EMP launcher or the rocket launcher into Grievous until he's dead. Either unit is useful for the next objective.

Destroy the AA guns
The obvious way to get to the Anti-Aircraft guns is from the ground. But in case you haven't noticed, there are tons of droids on the ground, just waiting to kill anything flesh-and-blood. So find the ramps near the west end of the hangar and go up one. Use your blaster pistol to clear out any enemies waiting there, and continue on to the very end of the platform. Now here's the tricky part: you have to jump down onto the beam that is just off the end of the platform. Once you're there, start firing at the AA guns. (Obviously use your most powerful gun.) When they're both destroyed, don't walk forward and fall off the beam to the floor if you can help it - the enemy units are still there.

Alternatively, just fire your EMP/rocket launcher from anywhere you have line of sight, close to the guns or not. If you're close, the guns will go down very quickly; if not, well, as long as no droid gets in the way of your rockets they'll go down quickly too. Also, note that the Republic Gunships you're clearing the way for don't just sit there; they'll fire on the guns on their own, helping you finish them off.

Destroy the Power Generator
There's a really easy way to do this. Whatever class you're playing (it doesn't matter), get in a tank, either the IFT-X that spawns near the Hangar CP (this is why you had to take out those guns) or an empty AAT, and set your sights on the power generator. Ignore everything else and just focus fire on the generator. You shouldn't have any problems at all with this. Destroy it, and the mission is over... now, prepare yourself for a more difficult one, this time against your former commanders.