Since I don't have any expenses I have to track for accounting purposes, I'm looking at this as a tool to track my own expenditure so as to help improve my spending habits. I realise the focus might be different so my suggestion may be useless to you!
What would be really useful to me would be reminders and notifications. With developing habits like this, I have a very hard time unless I'm constantly reminded. Like I take my lunch on weekdays at 12pm, so a reminder at half 12 or 1 would have me enter my lunch expenses. This could be further enhanced if you had a mobile app that used push notifications. This would be essential for me to develop the habit of doing it.