Cleared SCJP 1.4 on saturday with 88%,my experience was good,i was little bit nervous in the beginning, but once you start doing ques.it would be Ok.
Just keep the key concepts in mind, sometimes it happens that in trying to solve the tougher questions, u forget the basics!!
Solving mocks is important because during the first reading of the book(K&B) , u'll THINK that some lines or paragraphs are not important, BUT once u solve the 2-3 mocks and are on second reading of the book, u'll find that how did i miss these lines.
In short, stick to the objectives of exam ,study K&B atleast two times , and solve as many mocks as u can.I did not purchase any kind of commercial exam.
Already many people have given the list of mocks on this site, so just go through that, even i did the same...
On the day of exam>>>
1. Be patient and cool.
2. Read each question carefully.
3. Mark question if u have doubt in that.
4. Once u are done, go agn to the marked questions.
5. Revise all of the questions before submitting.
6. U'll definitely come out with a good score.
Hope this will help u..