As has been said, there's a big difference between a SECRET and a TOP SECRET rating. Where I work (defense contracting) the general policy is that you only get a TOP SECRET when required to work on a project that needs that level of clearance. Once the project is done, or you are moved, it is 'revoked' (can't remember the proper term for it).
For the secret, you're looking at about 25 pages of forms to fill out regarding your past history...scholastic, financial, etc., including the standard questionnaire (like the 4473) about drugs, criminal history, violent overthrow of the US, etc. You'll get fingerprinted and they'll do a background check, which depending on how 'backed up' processing is could take from 2 months to a year and a half.
headpulper is absolutely right on what can get you dinged. If you've had ANY documented drug issues you're pretty much screwed. I know from an old co-worker that they're a bit more lenient with bankruptcies dependant upon situations. They really only get curious moneywise if you have either a mountain of debt and haven't tried in good faith to pay it off, or if you're spending money like Trump without a documented income to support it.
Generally, if you've made an effort to keep your nose clean, stayed away from drugs, and don't want to piss off the gov't, then you shouldn't worry about the SECRET clearance. TS is a whole other ballpark. Those guys take it VERY seriously. Fine toothed comb seriously.