I don't think you necessarily need a brilliantly unique 'idea' as such, plenty of successful small businesses are not original, e.g. hairdressers/restaurants/holiday accommodation have been around for eons and you can still make money from them, but I do think you need to either offer something different/find a gap in the market AND/OR do whatever it is you do better/faster/cheaper/easier than your customers can find it elsewhere... simply starting with what you'd like to do rather than what you can offer is where some people fall down I think.
I don't think you necessarily need to be a brilliant business person right off the bat, if the business is based on some kind of skill or ability you have then that's a great starting point and you can learn the business skills necessary or buy them in (not many business owners fully understand all the ins and outs of tax, pensions and payroll for instance but a good accountant, payroll service etc can cover this for you, you just need to budget for it in your business plan).
If you want to make your business idea a reality I think I would start by drafting an initial business plan (not the 'nice stuff' about what the business will be called, what the logo will be etc, but the hard line of what your minimum costs will be, realistic turnover years 1/2/3 and onwards, market research, who your target market is and why they will want your product/service over your competitors, pricing structure etc) - then maybe try and find a good business advisor that will take a critical look at whether it's viable or not (you may have to pay for this advice but worth taking it upfront rather than jumping in with an investment you may stand to lose).
You don't say what kind of business it is but a lot of the successful business people I know started out running their business on a small scale and in their spare time to prove it worked and work out flaws/problems in a less risky way, before scaling up to making it their full-time employment - obviously if it's something like a restaurant or cafe this is harder to do but if it's a service you offer or something you'd sell you could maybe try working on it online and in evenings/weekends first - then if it works maybe aim to be able to go part-time in current employment in a year or 2, then eventually give up main job altogether? Also, again dependent on what the idea is, but it's a really good idea to get experience in the industry/area you'd want to work in first before going straight to being the boss, most people I know that have run successful businesses already had a lot of experience, not necessarily in running a business but e.g. have been employed as a manager in hospitality industry if they run a restaurant, are a builder/tradesman if it's letting out or selling property etc, this gives them the credibility they need with customers, investors, staff etc as well as confidence in their own decisions...
Good luck!