A lot of times especially for myself when I first started training and wanting to get my body in shape I would never warm up. Even playing basketball I would do two or three stretches then jump right in and play. Over the years I over looked the importance of a good warm up and this is why I want to help you. I find that we skip warming up for numerous reasons whether you are pinched for time or think you don't need to, it is something that I would highly recommend that we all do.
One of the benefits of warming up is that you prevent yourself from having injuries. I know this personally dealing with hamstring injuries if I had warmed up before hand and took the proper precaution and stretched properly I truly think that I could have prevented my injuries. Even until this day now that my body is healed I learned my lesson from before to never just jump into a workout.
Another benefit that warming up provides is the mental preparation part. Sometimes you may not be in the mood to workout so you find yourself not motivated to get it done. But I have found that if I warm up it sharpens my mind and gets me focused on the task that I am going to accomplish and therefore will put me in the right frame of mind. If the mind is ready to endure the discomfort from your workout then your body can prepare for the task at hand.
The last benefit that I have discovered from warming up is that it enhances your performance. During a warm up your blood flow increases which causes an increase in your muscle temperature. The more blood going to the muscles along with more oxygen available to the working muscles means better performance.
I would recommend that your warm up should be no more than 10-20 minutes. Some exercises for warming up are low intensity swimming cycling or running. Keep it moderately low so your body can adapt and get ready for your workout shortly after. You don't want to kill yourself during your warm up and then have no energy for your main workout.