It really depends on your lo's age.
Below 4-5 months, it's a good idea to watch your lo's sleepy signs, not the clock. After 4-5 months (after day-sleep development is over), you can start watching the clock a little bit more, but still watch your lo's sleepy signs. Biorhythmically speaking, around 9 am and 1 pm are the best times for naps, but again, it depends on how long your lo can stay up.
There is research to support keeping a sleep schedule. Really, it depends on your lo. If your lo is really schedule dependant, then a schedule might work. But if he's not, then it might not.
It's a little complicated...basically though, as the months of the first year pass, your lo will very slowly be able to stay up longer and longer. Your lo needs 16-18 hours of sleep a day in the beginning. Over time, that number decreases, until by the end of the first year, 13.5+ hours is about how much your lo needs a day. There's a sticky about it at the top of this forum (I think). How often you put you lo down for a nap depends on how long he can stay up without getting overtired.
What will help him sleep through the night is doing what you can to make sure he gets the rest he needs both day and night. Some lo's need less, others more. I would read through the stickies in the sleep and naps forums for more information, and keep an eye out for posts by other moms who are having similiar issues with sleep that yours is.
Hope this helps!
*HUGS*
Sonya =P