Jobs working for the US Attorneys Office or federal agencies (i.e. the SEC) are extremely competitive. In fact they're almost impossible to get right out of law school. Often they are coveted jobs from attorneys leaving the DA's office or large national law firms.
The best piece of advice is to go to the best law school you can get into, transferring to an even better one if you can (unless you can get into a T-14 right away of course).
Then again many people go to simply decent law schools and then go work for the DA's office (if hoping for a US Attorney position), become stars, and then rise up.
For SEC type positions, I'd imagine working for a national law firm would get you on track. To work for a national law firm, you'd realitically need to go to a Tier-1 law school.
I may be wrong on some of this, and someone with more insight would probably help. Any other people out there know much?