There are so many places to eat in Los Angeles that you can pretty much turn your head in any direction and see one or more from just about anywhere. If you're a die-hard foodie, then your whole Los Angeles trip may be based around some specific restaurants you have in mind, and for those, you probably want to make reservations before you leave home. Opentable.com is a good resource for researching restaurants and making reservations. For the rest of you, where you eat will be more a function of what attractions you're visiting and where you are staying.
To plan your dining strategy while in Los Angeles, take a look at my Los Angeles Restaurants page for resources on finding just the right restaurant for you.
If you're planning a special romantic occasion, you can go straight to my list of Most Romantic Los Angeles Restaurants with a View.
You might have heard about LA's mobile food scene, which has become a way of life for LA locals. You can track down the Top Gourmet Food Trucks in LA to see what all the buzz is about.