How can I build my full keyword list?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Jim Munro: I am a simpleton but I think your keywords should choose you rather than the other way around. Building value into your site to fulfill a purpose seems like a better use of your time until you have attracted an audience.
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  Karin Tierney: I like to use SEMRush to see what my competitors are ranking for and use those keywords :)
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  Dave Elliott: depends how much time you have. I really like grabbing all the semrush data for what i rank for and say 5 competitors, deduping getting rid of low volume keywords, then categorising the keywords, then running through rank tracking software to see what pages rank for what and then go from there. That process could easily take a few days though!
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  Jenny Halasz: That’s a good way to start.
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  Neil Cheesman: any `keyword list` will automatically come from the content that you have written and created for your website visitors...
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  Alan Bleiweiss: to be fair, if no content has been written yet, or if the content that has been written yet, was not written with at least a foundation of research into value keyword research combined with related entity understanding, then trying to make a keyword list based off of already written content may very well be dangerous.
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  Neil Cheesman: My point is really about knowing what the site is going to be about in the first place - which the Op doesn`t mention... my bad for saying `written` as this could either be in note form, offline, or even in the person`s head - but at least to have a baseline to start with - seems a bit chicken and egg - or maybe even seed and corn... and the corn may well provide the seeds for keyword ideas :)
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  Neil Cheesman: ps Google `Suggest` can be a useful free `tool`...
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  Alan Bleiweiss: So let`s be extra cautious here in our responses. If the content that has been written yet, was not written with at least a foundation of research into value keyword research combined with related entity understanding, then relying on third party keyword tools that use that site`s own existing rankings or own existing content as a starting evaluation point would potentially be a CATASTROPHIC failure. People need to understand how to perform proper industry / niche / market persona mindset word evaluations. If a site is not already doing very well for its most important topics, then just relying on current rankings and rankings of sites that show up based on what may be a very weak or inaccurate starting phrase set, is not likely to generate great results.So - research needs:1. Think about the offerings for that site. What are the main bucket (umbrella) phrases that you think, on your own, describe that site?2. Are those the words that other people, who are NOT in your business, use to describe those things? Or do those people use OTHER words to describe those main umbrella topics?3. Do you want to reach a diverse group of potential site visitors? This would include, but may not be limited to:A) Initial researcherB) Front-line decision makerC) Higher level decision makerOr alternately:A) ConsumersB) Business professionals A site can, and ideally needs to be able to use the words that each of those different types of people use when THEY think about whatever it is the site offers. And that`s just a surface scratching starting point in "persona" evaluations. 4. With that starting point list of phrases THOSE people might use to describe the overall topics for this site, then it`s a matter of doing keyword research using a range of tools, just two of which I like to use as my STARTING tools:Google AdWords Keyword PlannerMoz Keyword Explorer5. From there, I may go to any one of several other resources including, but not necessarily limited to:Google TrendsGoogle Search Results "People Also Asked" and "Searches Related To" lists of possible phrasesAnswerThePublic .com6. Using those tools, you need to also remember, along the way to ask "what are all the important questions people are asking about these topics?" Which of those questions are coming from people who are more likely to be my "ideal" visitor as opposed to someone using those words for other reasons not relevant to our goals?? Bottom line:ALL of the above can help not only provide the overall topics, but also the vast range of words people use in some way related to a site`s offerings. And there`s always even more that can be done beyond this list.
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  Neil Cheesman: Is this a new site? (I got the impression it was)
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  Alan Bleiweiss: Neil I wrote this not assuming it`s already existing, and that if it IS existing, the site owner needs to pause to think whether the content already there is overall well planned out for SEO reasons, and whether it is or not, I also made sure that this list is good to help go even further.
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  Neil Cheesman: And a darned good list it is too!
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  Jim Munro: ...building a better internet, one brick at a time. :)