When it comes to targeted search engine marketing and search engine optimization, you want to focus on the very best keywords first. That doesn’t necessarily mean the keywords that receive the most search volume. It could mean long tail keywords that are perfect for your niche and that see a moderate amount of search volume per month. It is much better to get the traffic from five long term keyword phrases that see 10,000 searches per month each or less than to receive the traffic from a broad keyword phrase that sees 250,000 searches per month but where the phrase is too broad for your niche. That isn’t targeted marketing.
But it really depends on the focus of your website. If you have an e-commerce website with thousands of product inventory then you could have a long keyword list. If you are a small business that provides a specialized service then your keyword list may be smaller. But the targeting for a blog and for a static website should be different.
With a static website you should build each web page around a primary keyword and a secondary keyword. How big your site is depends on your goals and initiatives for that site. But with a blog you don’t want to target more than a handful of phrases no matter how large your niche is. You may target phrases outside your core a few times here and there but by and large you should stick to a base keyword list. I’d say somewhere between 10 and 20 keywords and no more. That’s true targeted search marketing and it works.