Before the conference, you should do the following tasks:
Research and learn about your country's economy, history, foreign policy etc.
Follow the news and read articles from various newspapers such as BBC, The Guardian, CNN etc.
Pick an issue and do all the research that is necessary. Find out the UN's actions that have already been taken regarding this issue
Write a position paper that clearly defines your country's stance on the topic
Follow the guides on how to write a resolution
Using the research you have done on the issue, start writing your preambulatory clauses
Spend quite a while writing the operative clauses, because they do play a more important role. Remember that the whole point of writing a resolution is to come up with specific, new and better solutions to resolve the issue.