To prepare for Salesforce.com Certification exam the best resource to start your presentation is the Force.com certification study guide. There are study guides for each certification exam which will help you understand the course contents and weightage that each of the subject has in the exam.
The following are some important resources for the exam available online. You are advised to go through these resources few times each so that you understand the course contents well.
- Salesforce.com Help Site (use your developer edition to view)
- Force.com tutorial (iTunes)
- Salesforce.com Training presentations on Youtube
After you are prepared for exam based on the content specified in the study guide – you can take some of the mock exams available online. If you are scoring high in these exams you can go ahead and register for the certification exam.