The restaurant business is tough, but it can also be quite lucrative and rewarding. There are many things to take into consideration prior to buying, and many things to think about.

[edit] Steps

Choose your target client. Are you going to aim at a high turnover of pizzas to young professionals, or will you seek out a more mature and discerning crowd? A diverse and experimental menu might be appropriate in the latter case, whereas for the former a more traditional selection focusing on quality ingredients would be more suitable. Remember that younger people will eat out more and will see it as less of a special event – although they will rarely spend in excess of £15 or $10 per head. On the other hand, it is likely that they’ll spend less time in the restaurant so fitting in more sittings is a possibility. Older people will probably still see eating out as a treat or luxury and are likely to spend more in terms of both time and money.
Pick a location. Town centre premises with ample parking and a proximity to pubs or cinemas are usually the most successful, but are the most costly to maintain. The rents are higher than those located on street, but the turn out of customers will be higher as well.
Confirm that the area you choose has the demographics to match your intended client base. Do some research on household income and spending patterns for the neighborhoods you consider. Can they afford to eat out on a regular basis at a restaurant like yours, and more importantly, do they? There are loads of database services online that gather and sell income and spending data...it's well worth the cost of the reports to have that information in hand before you make a decision.
Pick a specific restaurant you want to buy. Before you introduce yourself to the owners, visit as a customer during different times of day to see what their trade is really like. Count tables, and try to estimate the cheque totals per table so you can compare that number to claims made by the sellers.
Make an offer to buy the restaurant. Check the books of the restaurant owners. Visit often to see how crowded it is, at various times of day. Look at the eating patterns of the customers and mode of dress.
Consider the cost. The restaurant may need substantial redecoration or equipment may need upgrading. Figure the expenses against what you think might be the income, depending on the customers you have seen, and the meals they have purchased.
Get the word out. While word-of-mouth is a restaurant’s lifeblood, advertising in local papers or distributing leaflets might be a necessity – especially if you are trying to turn around a flagging business.

[edit] Tips

As food becomes a national obsession, it’s hardly surprising that people are attracted to the restaurant trade.
Successfully running your own restaurant will provide you with that warm glow, as well as some financial rewards.

[edit] Warnings

Owning a restaurant is a 24/7 commitment. you have to be ready to devote your entire life to it, at least for the first year or two. Too many people see the fun and glamour, and don't know about the nights spent sleeping in your office because you're too exhausted to go home.
If you've never worked in a restaurant, hold off on buying one until you get some solid restaurant experience. Try to get exposure to all aspects of the business, from clearing tables to being on wait staff to kitchen, and ideally management (purchasing, hiring and staffing, scheduling, menu design, etc.)
Be sure to do solid business planning in advance of the purchase. Schedule a time to talk to a local business consultant like SCORE for free about the business.
Stop by the business at odd hours and actually count clients keep record of their orders. If you do some record keeping of this nature you'll be able to look at the books and see if they're true.