Google will show you many of the even obscure long-tail keywords you are ranking for already. Also, you will see the average estimated position you have for those keywords.
Go to Performance (the top graph on the homepage of GSC once you log in and choose the project you look at) > Full Report or simply the Performance menu item on the left side menu.
By default, you will see Queries sorted by Top queries, showing which keywords drive the most traffic.
This data is relatively limited according to many reports. Many keywords (especially local) are hidden for privacy reasons.
The keywords that drive the most traffic might surprise you. For reformas suelos baldosa example, you may rank well for off-topic content, resulting in loads of irrelevant traffic.
Look for relevant keywords with high potential and low effort.