The instinct is to sort a list by search volume and start at the top, and it is the single most expensive habit in this work. The biggest queries in any subject are held by sites with a decade of standing, so a small site sorting that way spends its year on pages that will never be seen. Finding the top keywords for you means the top of a list you have scored, and scoring needs your own numbers, not just the ones the tool supplied.
Start with what you already have
Two sources cost nothing and beat a cold list. Search Console tells you the queries your site already gets impressions for, including the ones sitting just off the first page where small improvements pay quickly. And your sales and support conversations tell you the words buyers actually use, which is where the commercially valuable long tail comes from and which no database will hand you.
Widen deliberately, then cut hard
Expand the seed list with a planner or whatever tool you use, but treat the expansion as raw material rather than a plan. Cut everything a person typing it would not want your page for, everything you have no standing to answer, and everything whose intent is served by a page you already have. What survives is small, and small is correct at this stage.
Score what is left on your own arithmetic
For each survivor: the searches you were given, the share you could realistically take at a position you could hold, your own conversion rate, and what a conversion is worth. That gives money a month per query, which is the only ordering that reflects your business rather than the tool's index. Doing this on twenty candidates takes an hour and routinely changes the order completely.
Write the top of that list, then keep the list
Take the highest few and write them properly rather than taking twenty and writing them thinly. Then keep the scored list, because in three months you will want to know what you rejected and why, and rebuilding it from memory produces a different list with the same mistakes in it.
Questions people ask about find top keywords
How do I find the best keywords for my site?
Start from queries you already show for, widen with a planner, cut anything you cannot answer or would not be believed on, then score the survivors on your own conversion rate and value.
Should I go after high volume keywords?
Rarely at first. High volume usually means strong incumbents, and a page that never gets seen is worth nothing regardless of the number beside the query.
How many keywords should a shortlist have?
Few enough that you will actually write them. Ten well-chosen queries you publish beats a hundred you file.
Where does Longtailo fit?
It does the scoring and keeps the shortlist, including the rejects and the reason, so the next round starts where this one finished.