I think the general consensus is that naps only improve nighttime sleep.
The many books on this will have sample schedules to try -- you don't need to stick to one but it would give you an idea of how much sleep is needed, how much wakefulness a baby can tolerate at various ages, etc. I found this was not necessarily intuitive to me.
I tried 4 books. I learned from each of them but haven't followed any of them exactly.
Healthy Sleep Habits, Happy Child by Mark Weissbluth -- he is a pediatrician, and pretty much a hardcore cry-it-out guy. I learned good information about sleep from the medical standpoint. He doesn't have a "method" or practical tips like some books have. You just shut the door and go in 12 hours later! (I didn't do this.) I'm joking, though, and his case for crying it out actually has some good points, although I didn't do it.
No Cry Nap Solution by Elizabeth Pantley I thought this would be the answer. Sadly, it didn't work for us. Again, there was some good information and I did try some tips on lengthening naps, but that was about it. Her methods take weeks to implement so it's hard to tell whether you're improving. Also, she focuses on "props" to lengthen sleep pram, car rides, swings. Ultimately (according to most books) these don't help a baby self-settle.
Baby Whisperer by Tracy Hogg -- she's kind of controversial, and I understand the people that don't like her. Her system is fairly formula-feeding-based. I bought her book because I thought it would be a middle-of-the-road method between "no-cry" and controlled crying. In our experience, BW meant uncontrolled crying! You stay with the child and help soothe it to sleep but it felt like I was just torturing DD. We faithfully implemented her methods for 4 weeks and saw significant improvement at night. Naps are harder to straighten out.
I think she has valuable information about schedules and sleep habits, and that her book would be more useful with a younger baby. (Mine was 8-9 months.)
The Sleepeasy Solution by Jennifer Waldburger and Jill Spivack -- To put it bluntly, when I got tired of torturing my whole family with Baby Whisperer, this book gave me the courage to do controlled crying. We've just started so I shouldn't comment but it's going better than anything else we've tried, and involves less crying than what we were doing.
I think it's easier to straighten out naps before habits get entrenched. I decided to just put it off when DD was 5 months and I think it ended up being harder on her to do it later.