That's not to say results can't be achieved tomorrow, they can .. read on.
The first test that an SEO campaign goes through is the test of your keyphrases against market data. What you are looking for first of all is to discover all the search phrases people use when they want what you sell, and there may be thousands .. it's a basic error to think there are just a handful.
Each one of those then needs to be checked that there are sufficient quantities of people searching on it in your geographic market to make it worthwhile working on, that you have the resources to beat the strength of competition, that you really deserve a front page place in search for that phrase, and that others are making money on that phrase.
Out of that analysis come some hot keyphrase opportunities.
Next up is working out which page of your website you want to direct each of those keyphrases to: your landing pages.
The next question is whether you are going to be able to sell things to people searching on each of those keyphrases, so before you invest in a medium term SEO campaign, run a pay per click (PPC) advertising campaign on your first chosen keyphrase to your chosen landing page. PPC ads can be set up in minutes and be running easily within an hour. Ballpark, you need a conversion (sale) every 200 clicks or better. If you get sales, you are then into the dual game of optimising your ads to get a great quality score and click through rates so your clicks are much cheaper, and using that traffic to improve your landing page so it converts better. Remember, when you start, you'll be spending more on the ads than you are making and there's a process to go through which may or may not end in PPC profitability but will, at least, end up in a reasonably good landing page.
If you can prove you are selling using PPC, your landing page and your chosen keyphrase, you can then move into SEO with the aim of replacing your PPC with free traffic. In the meantime you can keep running your PPC campaign or switch it off as you wish.
Since you are still testing, you'll be doing SEO on a single keyphrase group, but you really need not to write just about a tightly controlled phrase or Google will find you out .. it has to look like you are writing around a particular topic. So you work on that to build your inbound links while watching the number of inbound links you have versus your main competitor to work out whether you are gaining on them or not with the current level of activity. If not, push the accelerator harder and run for another three months or so.
Once you have your SEO position for that phrase, hopefully you'll have been testing another one with PPC so you can put phrase one into a holding pattern and start pushing at phrase two.
If a keyphrase makes money, there will be competition for it. Money matters to people. This is not easy. But millions of people do it, and this is how. It just takes enough resource and some patience, but once you have three or four top ranking, money making keyphrases you have a business and once you are in position it's much easier to defend your new online business.
If you are a small company reading this with not much resource, it's the same process you just have to choose a smaller niche where the competition is not so strong.