Lessons

Here's where I'd start:

• If you're new to competition math, start with the AMC 8 lessons. They cover the basic skills you need for the AMC.
• If you're comfortable with the basics, go through the AMC 10 lessons. They build some of the skills you'll need for harder AMC problems.
• If you're comfortable with AMC 10 topics, try the AMC 12 lessons. They add topics like logarithms, trigonometry and complex numbers, and help you prepare for the AIME.