Low is pretty much spot on in what he says; and that there is both good and ill-informed advice present, here.
What I am surprised I haven't seen mentioned yet (unless I missed it) is that USMC OCS is the only branch and program by which you can be *guaranteed* a flight spot. If you want to be a pilot; there is no better path. If you can pass the physical and academic requirements, you will attend on an air contract.
Now... on to the rest...
First and foremost, there are two basic ways to earn a commission in the USMC; attendance at the USNA or OCS. I went the latter route.
For the purposes of this discussion, when I say "OCS" I mean attendance at MCB Quantico; this includes PLC. The acronyms will get confusing (since OCS actually means two different things) so Ill keep it as simple as possible.
PLC is a dual 6-week program. "OCS" is a single 10-week program. I went the latter. I recommend the former.
Since you are still in your first year of college, PLC is still an option for you.
Given choice, PLC is preferable because of the shorter duration of each stint; in comparison to the 10 straight weeks of OCS (again, both being "OCS"). This is due to the physical demands and lack of recovery time.
Week six is about the point where you need that recovery badly. PLC allows this. OCS does not; four more weeks to go.
I was not prior enlisted but we had several in our platoon. All of them agreed that the physical demands of OCS were far in excess of those experienced at PI or SD.
As you will be expected to lead by example (OCS motto = Ductus Exemplo = "Leadership by Example"), your training is harder to ensure that you *can* lead by example in all cases. How much respect would you have for an officer who was at the back of the pack during a simple PT run?
The pace is non-stop, you will get very little sleep and your body will be pushed well beyond whatever preparatory training you did prior to arrival.
In concert with this, the mental games that the SI's will play with you are designed to push your level of tolerance.
In hindsight, the entire process is brilliant and one can see that every single step, no matter how small, is specifically designed to serve a purpose; to instill doubt, fear, confusion, etc. Your decision making and leadership abilities under that stress will be measured constantly.
While you are there you wont be able to see this.
A perfect (and literal) example of this blindness is the fact that you will not even be afforded the time or opportunity to observe your surroundings until about week three. Your eyes will be on the back of the head in front of you if they are not instructed to be somewhere else. Lord help you if you turn your head to look around.

The aggregate effect of the physical and mental demands add up to a very difficult program. The attrition rate is high due to both injury and expulsion.
OCS is different than the programs offered by all other branches in that the senior enlisted men effectively get to select their officers. You are primarily trained, lead and judged by NCO's. If they deem you unsatisfactory, they will remove you from the program by any means necessary. I recall several examples of readily identifiable weak candidates being subjected to treatment falling under that category which you would not see aired on the Discovery Channel.
In any event; here is the process:
1.) Locate an OSO.
2.) Submit application.
3.) If accepted, attend OCS.
4.) If passed, earn commission.
5.) Attend TBS (The Basic School; 6 months).
If you decide that, after exhaustive consideration, this is what you *want* to do, a few survival pointers:
Pre-OCS:
-Run.
-Run.
-Run more.
-Keep running.
-Circuit training.
During OCS... some for fun

-Any display of emotion is a weakness. Display none.
-Pace yourself when and where you can. You have nothing to gain except a broken ankle by being in the fastest run group during PT.
-Actors are not officers. Do not emulate Tom Hanks. This sounds so simple its almost stupid, but given the calculated lack of direction candidates are given, they are forced to draw from other sources of information. Movies are a popular choice.
-Buy a second pair of boots in Q-town during your first liberty. One for use, one for inspection.
-Lighters are more effective than scissors when removing threads from BDU's.
-Shoe polish is quicker on the naming stencil than the marker.
-The marker is quicker on the spade than soap and water.
-They are not sneakers, they are go-fasters.
-Making use of the 3-round burst feature on the M16A2 during field exercises is fun... and ill advised.
-Clearing leaves from the ground while providing security due to a tick sighting will make the Captain mad because you just gave away the position of the entire squad.
-A leg cramp is not a reason to rise from the prone position in the Quigley. Your company commander, who happens to be walking by when you do this, will inform you that he just shot you in the head and then ask you if it hurts more or less than the leg cramp.
-"Because I couldn't find a real job, Platoon Sergeant!" is *NOT* an acceptable response when the reasoning for your presence at OCS is demanded.
If you lose your sense of humor, you wont make it. Everything you do - even if you do it right - is a failure. Just keep that sense of humor to yourself.
SCUZZBRUSH BULKHEAD!
