Google will INDEX perhaps 1000s of characters in a title… but I don’t think anyone knows exactly how many characters or words Google will count AS a TITLE TAG when determining RELEVANCE OF A DOCUMENT for ranking purposes. It is a very hard thing to try to isolate accurately with all the testing and obfuscation Google uses to hide it’s ‘secret sauce’. I have had ranking success with longer titles – much longer titles. Google certainly reads ALL the words in your page title (unless you are spamming it silly, of course).
If you have original, quality content on a site, you also have a chance of generating inbound quality links (IBL). If your content is found on other websites, you will find it hard to get links, and it probably will not rank very well as Google favours diversity in its results. If you have original content of sufficient quality on your site, you can then let authority websites – those with online business authority – know about it, and they might link to you – this is called a quality backlink.
Forget whether or not to put your keyword in it, make it relevant to a searcher and write it for humans, not search engines. If you want to have this 20-word meta description which accurately describes the page you have optimised (for one or two keyword phrases) when people use Google to search, make sure the keyword is in there. There is more likelihood it will be used by Google as your snippet description in SERPs.
In addition to on-page SEO factors, there are off-page SEO factors. These factors include links from other websites, social media attention, and other marketing activities outside your own website. These off-page SEO factors can be rather difficult to influence. The most important of these off-page factors is the number and quality of links pointing towards your site. The more quality, relevant sites that link to your website, the higher your position in Google will be.