If I get my commercial pilots license and only leave flight school with 250 hours, how due I accrue the typical 1000 hours needed to apply for a fixed wing position?

How do you accrue the flight time required?

New commercial pilots can fly several kinds of jobs that will enable them to build up their flight experience to regional airline flight experience hiring minimums.

"Time building jobs" are:
Banner towing
Traffic watch
Skydive pilot
Pipeline patrol
Fish spotting
Ferry pilot
Flight Instruction (with the additional CFI license)

How do you find such jobs?
An aspiring commercial pilot would do well to network in the aviation community as they earned their ratings. Many employers will hire a face they know over a faceless resume. Chatting up pilots already doing these sorts of jobs provides a personal contact for the future. Banner tow & skydive operators can be found in the phonebook or online. This site provide some good advice for skydive pilots- http://www.DiverDriver.com. Call your local radio station and ask for the contact information for their traffic watch operator. Seek them out with resume in hand. Even if they aren't hiring at the moment, you will be a familiar face if you check back every month or so and they may consider you at a future date. Often the flight school where a pilot does their flight training may hire them to teach for their school when they earn their Certified Flight Instructor/"CFI". (You need this additional rating to be able to teach student pilots.) This link also provides some ideas for building flight time.

Once a pilot builds up the additional 750 hours above the 250 they had when they got their commercial license, they can then start to apply with the regional carriers. An applicant may meet the minimums, but depending on that airlines "competitive minimums", they may or may not be asked for an interview. While 1,000 hours is the least most regionals will accept, it may take a few hundred more to meet 'competitive minimums' to get the call for an interview.

To read about airline specific interview experiences, and what the applicants flight times were, visit this page-
http://www.AviationInterviews.com

New commercial pilots are also getting good kind of jobs these days. Try to get some more experience for the flourishing career. Answer given by av8trs is also informative and helpful. Go through it for the details.

http://www.commercialpilottraining.net/ProfessionalPilotPrograms/Commercial-Pilot/index.htm

The commonest way to do this is to get an instructors license for light aircraft, and accumulate the hours as an instructor with a small flying club.