In case you missed it from the news, here is a link to the scoring faq on SPOJ:
At present points are awarded to each user as follows:
* for solving classical problem p: 80/(40+number_of_people_who_have_solved p) points.
* for a top score in any challenge: 3 points,
* for any lower score in a challenge: (user's_score relative_to_the top_score) points.
So to earn good points on the site you need to solve some of the harder classical problems, or participate in the challenges / contests.
Also i like to note that currently only integer values are submitted in the score scripts, but we will probably change that to more accurate values.