Be your own guest first!
The best advice I can offer to anyone starting out and even for those who want to up their business is spend a night in your own rooms.
That way you will find out exactly what works and what is lacking - is the kettle cord too short?
Are the plugs in an inconvenient place and are there enough of them?
Is the room too light at night? You may need blackout curtains.
How is the shower? Water too hot or not strong enough?
Only by experiencing this for yourself will you find out your rental's shortcomings before your guests do.
Think of the things that you find convenient/comfortable when you travel and implement those ideas too.