Usually, it is easier to start from the system description or methodology. This section contains what you did yourself. So, it should be easier to write. If you have presented some of your work in lab meetings, use those slides as a starting point. If something gets hard to describe, consider using a diagram. If you re reporting lots of boring data, consider using a table.
After you finish writing about what you did, the experiments, and then the results, you can write a rough conclusion based on your results. Having done that, it is time to fill in the related research section. I will cover that in a separate section, for good reasons (you will find out later :-p).
Now have a good break, and read all of what you have written so far. Write a god introduction that prepares people to read all of that. A god introduction is like a funnel. It starts wide, with a sentence that describes something connected to a real-world problem. It ends narrow, with the readers knowing what they are going to read about.
If you have done all these, you can now write a good abstract. Write only WHAT YOU DID. An abstract is not an introduction or a survey. Be clear and brief. Present your best result in a concise manner. One way to do this is to end the abstract with a numerical result (Example: the proposed algorithm recognized 95% of the suspects in the FBI Most Wanted List).
You might have noted that I did not mention the paper length anywhere. If you follow the instructions, you will end up with a paper with a length that is not far from the page limit set by the conference. If there is a difference, it is time to edit the paper. I will cover that in the next section.