Before preparing title, keywords, description: Make sure you have your set of targeted keywords.
Preparing title, keywords, description: Do not stuff too many keywords; title should be up to 66 characters and 150 for the description. As for the keywords, I believe you can target as many keywords as you like the only problem is getting all of them rank in SEs
The reason why titles should only be up to 66 characters and 150 for the description is that how much Google will read/display the details of your site on SERP. Of course you can still stretch your title up to 100 characters but only up to 66 will be read and displayed, same goes for the description
