Reddit mentions of The Preservation Management Handbook: A 21st-Century Guide for Libraries, Archives, and Museums

I would suggest taking a look at the National Park Service's Museum Handbook (can download as PDF or view specific chapters). It's a pretty authoritative source and provides best practices for many objects/materials. It's kind of a beast to navigate but I can't tell you how helpful it is. The NPS also has a series called Conserve O Grams, which are shorter documents that discuss specific object mounting/handling/storing subjects.
Other online sources are the AIC Preservation Wiki and the NEDCC Preservation Leaflets, although these are more specific to documents and photographs. Might still be helpful though :)
My favorite book on preservation is the Preservation Management Handbook which is another text that is organized by the type of material you're working with.
Gaylord Archival also has some free resources on their website. I haven't reviewed these myself but they may prove helpful. Best of luck to you!