You can get different answers based on what 'value' means to you and that changes over time.
1. Value as in increasing the selling price of the prop - but you are not selling for at least a decade. Answer: Fresh flooring, paint, bath fixtures, updated kitchen. And the lights and switch plates like mentioned above. Cleaned up landscaping. At least 2 baths. Finished basement. New doors and doorjambs
2. Increasing your pleasure while living in it? Great kitchen. Nice lighting. Outdoor entertainment upgrades, new doorknobs. new switches, outlets and faceplates.
3. Increasing the rent. Fresh paint, flooring, add a bedroom - this can be converting a room so that it meets basic bedroom code - window, closet, door. 4. Increasing the speed that you can rent it? Get it super clean, no smells, new lights, switch and outlet face plates.
Soooooo. Have you ever been to a Habitat for humanity - Restore? , thrift store or second hand store? In the right area you can pick up "rental" quality and some times really high quality items on the cheap. Light fixtures, fans, even large appliances. One time I picked up an entire pallet of high quality white beveled subway tile for $300. Let me tell you lots of my rentals got pretty back splashes for little more than the price of mastic and a few hours of work.