Naming conventions help alot as well as a very structured folder system. The other thing that saves me day to day are send alerts for QA errors. Allows me to consolidate all of the issues as they occur and ensure issues are fixed.
I'm a big fan of daisy chaining campaigns together with the "Request Campaign" action. This has allowed me to isolate the parts of our campaigns that happen over and over (like alerting the salesfolk to interesting activity) and call them up whenever I need them, versus recreating those actions over and over in individual campaigns.
I also like "Request Campaign" because it allows me to get a little fancier, logic-wise, that I could with just the Choice options for different flow actions. I'm looking at you, insanely intricate lead routing rules for demos that require me to set different options based on location AND company size!
We have quite a few users in and occasionally we lose some... consistency... in how programs are crated or leads are uploaded/edited. I keep a few campaigns and smart lists the I check weekly to help maintain our data. By checking it weekly (or so) I can fix issues before they get out of hand and "re-educate" anyone who is working outside of our best practices.
In Design Studio - Mass approving email and landing pages makes the building process so much faster. I love this feature.
As our team and company grows, the folder structure can get out of hand quickly. Something that has really helped the team keep track of programs is an "Active" folder for each region. This way we know which programs need updating or where that random alert came from Once the program is complete it gets stored in the quarterly folder until we archive. So much cleaner! Plus, this has really helped with onboarding new folks.