Salvation is necessary for all mankind (Rom. 3:23), who, due to the presence of sin in nature and action (Rom. 5:12-21), fail to meet the required standard of perfection.

Salvation is by the grace of God. (Eph. 2:8,9 Rom. 3:23)

Salvation is received through faith in Christ Jesus. (Gal. 2:17,18 Rom. 3:28)

Opinions :

faith
it is my opinion that most people misunderstand salvation because they misunderstand the word faith. faith is not an irrational belief; nor is it just the holding of a dogma or idea as truth. faith requires an idea to be held as truth - but the focus of the word is on the action/reaction to the idea.
before everyone runs to the dictionary, let me hasten to add that the definition i am expounding may not exactly sync with the current english usage. i'm hoping to come nearer to the mark on the greek word as used by the authors of the new testament; if you'd like to get a picture of how they used the word, look up all the usages of the greek word pistis (in all its forms) and piece together your ideas from the context (this is really an exercise that every christian should do; sooner, rather than later, as it's a rather crucial word).
the most obvious place you can see that the new testament's use of the word faith is focused on the action/reaction to the concept is james 2:17-20. consider that a headstart on your word study.
there really is a lot more to say on the topic of faith; as such, it has been split out into its own document.

predestination vs. free will
this is really a virulent topic. i'm afraid that i'm going to anger someone, so let me start out by stating very clearly and definitely that i may very well be wrong - i'm open to that.
in a nutshell, i think that both predestination and free will are correct, but that such an opinion doesn't make very much sense.
the long version is much more offensive, especially on the predestination side. there are two possible types of predestination: infralapsarianism and supralapsarianism. infralapsarianism holds that the act of predestination happened after mankind had already sinned and fallen. in other words, the predestination is an act of redemption alone; no one is predestined to hell. on the other hand, supralapsarianism is the idea that predestination happened first, before the fall; this would involve a predestination to heaven and hell. i personally think that the bible teaches supralapsarianism. the reason that i actually adhere to such a stomach-wrenching idea is romans 9; i can't get around it. and i'm not just trying to be offensive. it should also be noted that the majority of calvinists adhere to infralapsarianism; supralapsarianism is nowhere near as widespread.
predestination (summary of my beliefs) -
1. God chooses salvation or damnation for all people. absolutely.
2. God isn't just saving some from an already damned mass of humanity. the concept of 'vessels prepared for destruction' seems biblical.
so...now that i've established just how rabid the predestination side is, let me coax the lamb to lie down with the lion; i also honestly believe that bible teaches that man is able to choose salvation (sorry about the contradiction with the above set on predestination. it really doesn't make any sense to me either, but save those thoughts for the last section please). there is a definite biblical focus on entreaty towards obedience/salvation (gen. 4.7 etc) and a definite judgement for man (a concept associated with freedom); all concepts that show god acting as though man is able to determine (and is responsible) for his actions.
i think that the idea that both predestination/free will are correct is similar to the concept of sanctification, another idea which ties together the work of god and man. and while it doesn't make sense, honestly, i don't think that there is any way to tie the involvement of a omnipotent being who is outside of time with our universe and have it make sense (it's the problem that they touch on in time- travel movies, extended and extrapolated a whole bunch). so the only question becomes what does the bible teach on the subject (since this is a christian theology...).