I took a long time studying as I had to do so between work and other stuff.
Also took a little time to save up and purchase 2X3550s and 2X2950s to practice on. I got those on eBay.
I took the SWITCH class which helped get me going. The books also have practice questions at the end of each chapter and the lab guide is also really good.
I also bought the Cisco Press SWITCH Official Certification Guide. I usually like to read both because sometimes the Cisco Press is more readable and explains concepts a little more deeply.
The practice test it comes with helps assess where you're at but I tried to stay away from that because it can give you a false sense of security once you've memorized some of the questions.
As much as I could, I also tried to read right from Ciscos website articles that had to do with Understanding and Configuration. I created a list of articles I read at least parts of http://itprostuff.blogspot.com/p/ccnp-switch.html. I really like doing this because it helps get you used to the language Cisco uses and the way they describe concepts, solutions, etc. As with any vendor exam, you have to learn how they think.
I used the Boson Network Simulator some, but kind of abandoned that due to some fo it's limited functionality. It worked fine helping me prep for the Route exam and I plan on using the labs it comes with a lot for the TSHOOT.
I used GNS3 some to practice stuff that wasn't specific to Swtich and could be configured on a router also.
I used free practice questions and helpful videos here on the Learning Network site.
I spent time practicing on other equipment other than my own at packetlife.com.
Their are also good CCNP Guides available if you search Google. I think some of them are really helpful when you're getting close to the end and you just need to remind yourself of all of the material. I found a good one I paid a little over $20 for all three exams that was well worth the money.
Last but not least, answers here on Cisco Learning Network can really help too. Some of the people that comment on here and answer questions are really great.
In short, get as much hands on and reading from as many sources as you can until you're absolutely sick of studying