There are a few things that all people should know before entering any sort of the Military. The most important of them all is, 'is this truely right for me?'.
Sure, the question seems easy to answer, but many people find themselves stuck in a position, after joining that doesnt seem to please them; and by then, it's to late. You must remember, once you sign your contract, pick your MOS (military occupational specialty), and take the military oath, your in. That's that. Now are you still interested in being the best of the best?
If you still are, then listen closely...
It all starts off by talking to your local recruiter. Schedual a time to meet, and talk to him about your interests. If anyone can tell you what to do and how, it will definitly be your recruiter. Some recruiters may challenge you to think about other options in the military that also fit your interests, don't ignore them. Your recruiter know whats best, but not always whats right. If you still plan on joining the Rangers, good.
Now, after you've talked to your recruiter, he may of or is planning on having you take a pre-asvab. (this is the armed service aptitude test). It asseses your knowledge in algebra, word knowledge, mechanics, paragraph comprehension, etc.) The higher you score on this, and the real thing, the better off you are to having a successful life in the military.
One word about the real test... Study!... and don't forget it. You must score high on this test to become a ranger. There are many books you can purchas that can aid you in studying, that specificly target questions that relate to the ASVAB.
Now after you have been studying, you and your recruiter have two options, you can go down to the nearist MEPS and take the test, or you can go to MEPS and take the test and the physical. (upon passing the physical you pick your military job). Either way, if you have tested with a high score, from studying, and passed your physical, you are on your way to the rangers.

Picking your MOS: Now, when you pick your MOS, you sit down, and talk to a military councler one-to-one. He or she goes over what MOS's are available and are according to your test scores. The earlier your test in the year, and the earlier you pick your job in the year, the more likely you can pick Army rangers as your MOS. You see, there can only be a certin amount of people for each consessive training season, it's a first come, first serve basis, and the training slots do fill up fast. You will also discuse how much money you will get as a sign on bonus. Depending on the job, and how many years you sign on for, it may range from $1,000 - $30,000.
So what happens if all the training slots are taken for that year? Well you can always wait for the next year, and hopefully get lucky. But most people, after going this far, don't wanna wait a whole year before picking a job again. in this case, you can always join another MOS, and apply for ranger training. This was the most commen way of joining the ranger training prior to 2004. It has been only recently that you can reserve a slot in ranger training.
A few good options for the other MOS might be infantry, or support infantry. This is because they go through a hard, but not impossible, training program that gains confidence in most soliders. This is perfect for someone who wants to become a ranger. The infantry, in a sense, is a dumbed down ranger.

If you have signed up for any part of the army, reguardless of the rangers or not... START TRAINING. I cannot say this enough. There is nothing worse then a soldier in training who cannot complete the aquired amount of push-ups, or cannot run a mile in 8:30. The mor you train prior to your actual service, the better off you will be. Ranger training is said to be 80% mental, 20% physical, but if you train before entering, those statistics tend to look more in your favor. So...
Now, if you have made it this far, and have signed up and ready to go... then Congratulations. You've entered the United States Army and on your way to becomming one of the most elite forces in todays military. Live up to the values of these soldiers, for the Training, Missions, and Prior History makes you for who you are.
Once again, congratulations...