Learn and practice your major and minor pentatonic scales. Pentatonic scales make up most lead guitar parts and guitar solos in rock, jazz, country and blues music. A major pentatonic scale is root note-2-3-5-6. In the key of C that is C-D-E-G-A. A-minor pentatonic scale is root note-b3-4-5-b7. In the key of C that is C-E-flat-F-G-B-flat.
Learn and practice your melodic minor scales. The melodic minor scales are used quite frequently, though less than pentatonic scales. A melodic minor scale is root note-2-b3-4-5-6-7. In the key of A that is A-B-C-D-E-F-sharp-G-sharp.
Practice your scales with a metronome or rhythm machine. Learn to play in common time signatures like 4/4, 3/4, and 12/8. If your metronome or drum machine allows you to alternate between time signatures, set it to change to a different time signature after a certain number of measures. This will help you get better at counting measures and help your understanding of time signatures and how they work together.
Practice with other musicians as often as you can. Joining a band or a group of musicians who have just started learning their instruments can help you practice in a comfortable environment. Practicing with more experienced musicians who are willing to help you learn can help you greatly as well.
Record yourself playing with the metronome or rhythm machine on an inexpensive multitrack recorder or computer recording system. Listen back to the recordings you have made to evaluate your performance, and use the recording device to help you figure out what areas you need to work on.
Learning popular songs that you like is a great way to learn lead guitar parts. There are many sheet music and tablature books available that can teach you lead guitar parts through stores like Guitarcenter.com and online stores such as Amazon.com and eBay.com.