Prioritize RSS usage only on the key buildings at first. Key buildings are those that are needed in order to upgrade your HQ.

The Tech Center upgrade is required every level. The other buildings rotate between levels.

They are:

You don’t need to level every building to max in order to get HQ 30.

Building Max Level for HQ 30
Tech Center 29
Tank Center 28
Drill Ground 29
Hospital 25
Barracks 27
Wall 26
Alliance Center 23

Once you reach HQ 30, continue to level buildings as RSS allows as HQ 31-35 will be available in a future season.

Getting RSS