This is a guide to the more common shots I find myself taking when I'm using the M203 on Sinjar. Keep in mind that I'm not showing you ALL of my tricks (I like to play as an Insurgent sometimes, too), and that this is not an exact how-to, it's just a general guide. You may need to change where you aim a little, but for the most part, this works.
This is the first spike-thingy on the way to A.

The most you can really do here is to clear out the right house:

This is from that wheel barrow thing:


Now, this one is my favorite to clear the right house. You can launch a nade almost anywhere in there by changing your aim a little, and it's almost impossible for them to step out and hit you without getting shot themselves.


And from around here (look at the house for an idea of where you are) you can blow up the glass house:

But don't think I forgot about that bastard in the other house. From this bunker you can use the top bar (put the top at about the middle of the window) to most likely get rid of him:

Moving on to the road to B:
From behind the rock you can get rid of any harassers in the cracked house easily:

But your biggest problem is the people on the bridge. This will clear out around the middle of the bridge...


...and I seem to have misplaced the pictures for getting the back part of the bridge, but it's not that hard, just adjust your aim.
And from here it's easy to clear out Bravo:



And once you get to Bravo, there's usually Insurgents camping around the hill and giving you a hard time. Destroy 'em from the window.

This will hit around the center of those ruins.

And this will hit the balcony overlooking B. You can adjust your aim a notch lower and hit the house to the right of it.

And onward to Charlie...
On the edge of the balcony overlooking C, you can hit...
The window...

That hallway by the stairs...

That house way back there...

...And this will hit most of the things over there.

And from the end of the hallway, you can hit the door on that building (Which you will want clear, as it's an awesome position giving you a VERY good view of D, which I will address later.)

And someone always seems to be around there -

And from here -

- you can completely dominate D, dropping back to either C or that house with the hole in it to rearm.
The pillbox

The top of D

The fenced in area of D

Those are what I use most, and they seem to work pretty well. If you're under fire, what I do is remember the target's position, crouch behind cover, guess it, and shoot. It works better than you'd think. I made this by myself, and it didn't take very long, writing this was actually the longest part of it. If you want to learn the M203 really quick, start a server on the map of your choice, go to the console and type in sv_cheats and give_ammo 40mm. You'll get 40 nades, and you can practice to your heart's content.
I might do some for other maps/give more detail on this one if enough people ask me and tell me the map they want.
Ammo caches:
There's only 4 ammo caches that I'm aware of, and I'll tell you the routes I use to get to them.
Heading to alpha:
You're pretty much fucked when it comes to getting more ammo here. The best thing you can do after you run out of ammo is to run up into the action acting like a normal rifleman. The nearest ammo cache is the building in the down, near the wall that's being built, and there's a pretty good chance that someone is somewhere along that route, so it's not really even worth it.
Heading to B:
Here, you have some choices. You can go to the ammo cache near the original INS spawn, but there's a really good chance that an insurgent is watching that area, so you want to be sure that it's clear. You can also go to the place that I described for A, and this time it's more likely that you'll survive going around the road. But if you're close enough to B, and there isn't heavy resistance, you're best off joining the assault and going in to cap.
Going to C:
This one's really easy, you don't even need to walk very far. There's a cache in the building by C that you can use, and if you're around C, blowing shit up, you can easily walk into the building and rearm.
Going to D:
You can go to the building with a hole in the top, or back to C. The first one will likely be faster, but if you head to C you will be less exposed to enemy fire.
What you need to do:
A: Your primary concern is clearing the houses and the sandbags. after that is done, head up to cap.
B: You need to focus on keeping the bridge clear. Wait until you know where a sniper or MG'er (preferably a group) is on the bridge, and then fuck him. (and everyone near him, if you're lucky) After you run out, you can rearm or head to cap. It's your choice. And also, if you have an opportunity to go up to B and cap it, and you still have nades, go for the capture.
C: Use your GL to take out any tricky targets that are outside of B. But when you get into the town you will be better off using your rifle because of the close quarters of the area. If there's a (multiple) dug-in target(s). Then use your GL, but for the most part, just use your rifle.
D: Now THIS one is some fun shit. There's a lot of insurgents all over a relatively small area and you have long-range explosive power at your disposal, so blow some shit up and have fun!

(By the way, does anyone else think that the devs designed D so the marines could have some fun shooting the proverbial fish in a barrel, when the whole round THEY'VE been the [again, proverbial] fish?)