We updated a rental property to sell it a few years ago. We did some very cheap things to make it look better, which worked really well.
We had put a new kitchen in, in 2007, which was still in good condition, and although not the ‘latest trend’ still looked good. In one part of the kitchen that didn’t have fitted units in we improvised a ‘breakfast bar’ with an ikea table / desk top on adjustable legs, and two saddle-style stools, that made it look much more like a modern kitchen!
The bathrooms were white fittings / fitted units that had been fitted in 1997. Still in good condition, but looked very dated, but I realised it was the older, chunky rounded taps on the sink and bath, and the round white knobs on the fitted units that made it look dated. So we just changed the taps for modern ones, and put stylish brushed steel knobs on the cupboards. Really quick win.
Re: the paintwork, it looked quite battered / dirty / old. But, before going ahead with a full redecoration, I cleaned all of the walls with sugar soap, and we only had to touch up a few small places with matching paint. Again, I realised that the thing that made it look really dated / aged was the paint on the woodwork (skirtings and door frames and window ledges), as it was chipped, scratched and quite yellow. So I got a pot of one coat egg shell in brilliant white, and over the course of a week or two worked my way round the house just putting a new coat of paint on the skirtings, door frames and window ledges, in all of the rooms. It made an amazing difference! It smelt of fresh paint, and even the estate agent (when viewing it) said ‘oh you’ve completely redecorated’!!
In terms of the carpets and flooring, I would be tempted to get them all cleaned (maybe hire a cleaner machine?), and see if they could be re-stretched by a carpet fitter.
I bought some pieces of furniture (mainly from eBay, but some also temporarily taken from our house) to dress the house for selling, and added nice rugs. If you add in things like plants, a few pictures and some brightly coloured things (like a vase of flowers, or a fruit bowl, and lamps) as visual focal points to the centre of the room then you can completely draw the eye away from the age / condition of the carpet.
In our experience, making the photos on the listing look really good (rather than just an empty room with new painted walls and new carpet) gets more people viewing and helps it to sell a bit quicker.
I am slightly addicted to eBay, so I am quite good at getting really lovely furniture at a really low price! The buyers actually asked to buy all the furniture off us as well, so it all worked out well!