Most of the methods of improving the appearance of your house discussed here require time more than money. If you can't sell your house without doing some major improvements, you might need to reconsider whether you actually need to move.
The exterior of your house is the first thing visitors will see. Even before they make an appointment to actually view the property, the external appearance of your house can attract ir repel potential purchasers. Don't have bags of rubbish or overflowing bins standing around outside. It can even be worth cleaning the street or pavement area outside your property, even though it isn't actually yours.
Gardengrass, if any, and keep any flowerbeds neat and weeded. If there are any dead plants around, even in hanging baskets, remove them. If you have pets, ensure that you've cleaned up after them.
Large trees that overshadow the house, especially those like conifers with shallow root systems, are a potential problem and should be removed if possible. If a potential purchaser commissions a survey of the property, trees that could potentially fall on the house and damage it will be highlighted. Trees whose root systems could get into the foundations and cause subsidence will also be pointed out. These can then lower the price that a purchaser is advised to offer, and there may be problems with the buyer obtaining insurance and a mortgage.
Fencing, Walls and Gates
Make sure these are in good repair, and painted or creosoted if applicable. If you have hedging as a border, keep it trimmed.
Keep all the windows clean, and any external paintwork fresh, whether on window frames, doors or walls.
Make sure all woodwork is clean, and that the paint looks new. For walls, it is best to go with paint, especially the simple, if boring, magnolia.
Decoration will quickly, if somewhat irrationally, put people off. A lot of viewers will look at brightly coloured walls, whether painted or wallpapered, and be put off from making an offer. Many people cannot see the potential to change the decoration, so, even if you personally like bright pink walls, you are trying to sell the house so you want to get as many possible buyers as possible, rather than have viewers look and think "I'd be interested in buying this, but I don't like the colour." It may seem amazing, but something as simple to alter as this will put people off.
Using magnolia presents a "blank slate" effect. Its very blandness allows people to project their own image of how to decorate the house onto it. You could get a similar effect with white paint, but this gives the house a cold feeling, and the unwanted reaction here will be for people to consider the house to be cold and unwelcoming.
If you have any furnishings or decorative features that are not typical, you are advised to remove them. You don't want things that you believe precisely reflect your own personality, because you are selling, not buying, and outré furnishings will reduce the number of potential buyers. Bold colours on built in furniture can also cause problems.
Clean and Tidy
It should go without saying that the house needs to be clean and tidy. Clean the inside of your windows, and wash any nets. Vacuum the floors, and dust the surfaces. Even if your house is normally in pretty good shape, give it an extra going over before people come to view it, especially if you have pets or children, both of which can dirty up a house pretty quickly.
If you have a breadmaker, you could always try baking bread - it does work for supermarkets, but may be a little obvious in a house.
If you want to sell a house quickly, you are more than likely going to have to sell for less than you want. As well as getting valuations from estate agents, look at other similar houses in the area. What are they going for? Do they have any features your house doesn't, or vice versa such as a conservatory or loft conversion? Are they in better or worse condition? You are going to be looking at a price in the lower end of the range in your area. Yes, your house may (technically) be worth more, but that doesn't help if you need a sale and trying to get what you think or have been told it's worth takes months, or even years, longer than planned. An item is only worth what someone is willing to pay, and if no one will pay the asking price, it isn't worth it.
Don't necessarily trust the opinions of estate agents; many are not really qualified to value houses, especially those working for national agencies tied in with a mortgage company.
The image you are aiming at is that of one of the better properties in the area, whilst also being one of the cheaper ones. You could go for both best and cheapest, but this will cost, both in improving the condition of the house, and lowering the money raised from the sale.