Most septic problems are caused by neglect rather than misuse, but a handful of habits do real damage over time. These are the ones worth changing.
Wipes, Even the Flushable Ones
Flushable refers to whether it clears the toilet, not whether it breaks down. Wipes stay intact in the tank, add to the sludge layer faster than anything else, and are a common cause of pump and filter blockages.
Grease and Cooking Fats
Grease cools and rises into the scum layer rather than breaking down. Enough of it and the scum layer reaches the outlet, which is the point solids begin travelling toward the drain field.
Harsh Cleaners in Quantity
Normal household cleaning is fine. Pouring bleach or drain cleaner through the system regularly is not, because the tank depends on a bacterial population to break waste down.
Garbage Disposal Waste
A disposal does not remove food waste from the system, it just makes the pieces smaller. Households using one heavily need pumping noticeably more often.
What Does Not Matter Much
Normal toilet paper is fine. Laundry detergent in ordinary amounts is fine. Additives claiming to replace pumping do nothing useful, and some marketed as drain field restorers can make things worse.