A useful service entry is short but precise. If you only write 'oil change' and the price, important details are missing. A few months later you may no longer remember which oil was used, whether the filter was changed too or where the job was done.
The most important fields are date, mileage, work performed, price and notes. If the work included parts, it is useful to list those too. For example the oil filter, cabin filter, brake pads or a specific fluid.
If maintenance was done at a workshop, add the workshop name. If you did the work yourself, note that as well. It helps later when you want to remember under what conditions the work was done and who to contact again if needed.
The more consistently you fill in entries, the more valuable the full history becomes. The goal is not to write novels, but to keep the right facts.