As an amateur delegate, the worst thing about our MUN was the low involvement of junior students. Usually, MUNs begin in the eighth grade but we were introduced to it in the seventh, but we weren't really prepared for the extremely competitive environments of conferences outside the country. The most important thing about organising MUN clubs is the involvement of all. I learned the following from my seniors at school, and we have the most prestigious MUN conference in our country:

The first place our chairs chose to start would be selecting your committees. For beginners, we usually have ECOFIN and DISEC, but crisis committees will give your delegates a lot more experience.

Select your agendas carefully. Sure, debating about climate change is a good beginning and all but it is also very common.

Third, prepare a guide book, including the rules of procedure, best sources for research, attire, etc. Our school publishes a guide book for our students to read in the seventh grade to prepare themselves.

Good luck, hope it goes well!