Shoot for the attainable. Action sequences involving car crashes and explosions might seems like necessary elements of your film, but spending money on set pieces and dressing takes money away from more important elements. Good low-budget films focus on locations and props that are cheap and easy to access and film.
Get volunteers. Many people will work on your film for free, simply for the novelty of being on set. Choosing people with a willingness to be on time and work through the day can more than make up for lack of experience. If your area has a high school or university with media classes, contact the school administration. Students often are willing to work for nothing more than the experience.
Spend the most effort and money on your cast. A good actor can save bad lighting, poor camera work and muddy sound, while a bad actor highlights all of those elements. The success of an entire film can hinge on a performance, so make this the one area of your film that doesn't look low-budget. Spend time casting appropriately. Pay your actors as well as you can and treat them respectfully. Rehearse thoroughly and give actors the time, space and direction they need to develop their performances.
Plan every moment on the set. As soon as you start rolling the camera, you start burning through your limited amount of money and time. Spend the time before production to plan where you'll be, what you'll be shooting, who needs to be there, what props you need and how long each scene should take. Budget time generously; you'll always need a few more takes than you think.
Only buy what you absolutely need. A film shot entirely on a camcorder and edited on home computer software doesn't have quite the sheen of a more expensive production, but if those elements are the only available solutions, use them. Better to finish your film using the cheapest possible gear and smallest possible crew than end up with a film only half-finished because you can't afford an editing suite or can't pay your workers.