What Spendius said.
Timing is important. A severe recession when people are not spending money on non essentials (i.e. eating out) is probably not the time to start a new business with an optional product.
Location is critical. You can have the best restaurant in town, but if it isn't easily accessible and people don't feel safe going to it, and at same time the land cost/construction/and/or rent is not affordable, you have two strikes against you right away.
A good business plan is important and a vision of what you want to be. Low end casual? A nice but inexpensive place? Fine dining? And keep the menu limited to popular items that your chef and helpers can learn to prepare and serve competently.
An excellent business head is critical--being able to fully analyze the full cost against price, the cost of licenses and taxes, the cost of insurance, the cost of portions, the cost of 'freebies', the cost of waste, the cost of labor, the cost of overhead and knowing what price you can charge that people will pay and cover all your costs plus produce a reasonable profit for yourself.
An eye to visual aesthetics and appreciation/expectation of excellence in your product. Otherwise the requisite repeat business will be hard to come by.
A sufficient and competent labor supply is important. Unless your employees share your appreciation for cleanliness, aesthetics, quality, service, etc. you'll fight an uphill battle that you will likely lose.
Do all that and you should succeed, but its by no means a sure thing.
Skip any steps and the odds are strongly against your success.