If it hasn't been kept up, first thing to do is go into FORTRESS and make sure files are fully up to date - awards, qualifications, organizational groups (platoons / divisions / flights as well as optional groups), personal information (if you're experiencing issues, it can be good to re-run validations for specified or all cadets), everything. Checking Cadet Information Cards with the cadet (similar to verifying ones' MPRR if you've done that before) can be a good way to do this, though it can be arduous if you're with a large corps / squadron; in those cases, having a level officer or platoon / division / flight officer review them with the cadet then returning for any necessary corrections can be useful. If corrections go back some time, you may need to initiate FORTRESS Data Modifications to have them corrected appropriately. Doing that is preferable to inputting incorrect information (which can result in cascading issues) or just incorrect information (which may result in cadets not getting what they've earned or conversely receiving recognition that should have gone to another cadet - admittedly a less frequent one). If you're with an army unit, don't ignore the NSE program in this step.
Make sure your paper files are up to date with required documents as well. Print anything that needs a paper copy filed and ensure it's posted to their personnel files.
Keep administrative documents ready to go for the unit. Pay sheets with tombstone data, claims, any paperwork required by RCSU, keep that stuff ready and/or moving as needed; the more you can have prepped for people and the less you need to push off to them, the better. That said, don't feel like everything has to fall to you - if you're overtasked, let your CO know; it's part of their their job to ensure you have support as/if necessary.
Develop a plan for the year for administration as a whole. Include enrollments (peak in September / October but ongoing through the year), annual validations / DHQs (September-November, but ASAP), CTC applications (unclear when this year due to changes with rescope), CTC travel, end of year award input, etc. Know your role for those - enrollments must be approved by CO but you can input once approved, you can normally fully handle annual validations, DHQs are to be sealed and sent directly to RCSU without review at corps level, CTC applications often initially entered by AdminO but CO has to do the ranking and recommendations, etc.
If you're sending paperwork outside the corps/squadron within the CAF (RCSU most often, but other corps/squadrons and other CAF units may happen as well), ensure you complete a DND 728 Document Transit and Receipt; while paperwork generally gets processed anyway, having that can increase the likelihood it doesn't die on someone's desk, and if it does, it provides proof that you did indeed send it.
Beyond all, if in doubt, ask. Your CO should be your first point of contact for most things, but if you need more help approach your network of other CIC / COATS personnel, your Zone Training Officer, etc. Your CO may want some modifications to what I've said above as these are general good practices but are not always applicable; defer to their direction.
Let me know if you have any questions; I'll try to help as best I can.