Imperial Standing are items that you need to build buildings to level 10. These are player suggestions on what you should use your imperial standings on.
LEVEL 10 BUILDINGS It is not written in black and white what you should upgrade first when it comes to Imperial Standing for level 10 but here is the generally preferred way.
1. Academy - Researches don't require Imperial Standings so this is a good place to start as it offers so much more once you've got it. You may be required to upgrade buildings for some researches (farm for irrigation for example) but around half require no level 10 buildings.
2. Rally Point - This allows you to send 200,000 troops per march rather than the measly 150,000 at level 9 and allows you 12 marches at a time rather than 9 at level 9, meaning that when you have level 10 Palace you can reinforce all your wilds and still have 2 marches at a time.
3. Palace - You get yet another 3 plots which are invaluable as your upkeep starts to kill you, and another wild slot for that level 10 that will help there too.
4. Watch Tower - It makes you virtually invulnerable to scouting (exempt of level 10 stealth) which is very off putting to attackers.
Past these 4 you should simply get whatver level 10's you need to research. DO NOT use them in multiple cities for the same things until you get spare Imperial Standings.
A lot of players seem to dream about level 10 Apocothary. The fact is that at level 9 you get 50% wounded rather than killed and at level 10 you get 60% - the difference isn't really worth it.