Traditionally, choosing phrases and idioms as examples for a dictionary headword entry is largely based on the lexicographer's personal experiences or impressions. Choosing them according to frequency usage should be the new standard in future lexicography.

Wictionary for Spanish echar currently lists 112 derived terms, 107 of which are phrases or sentences. I use Google Ngram Viewer to check the usage frequency of 96 of them, after removing 11 that have a length of 5 or more tokens, the maximum allowed by the Ngram Viewer. The following are the idioms with a frequency higher than about 0.0004:

echar de menos, e.g. te echaré de menos (“I’ll miss you”, literally “I’ll find you missing”; etymologically echar here is a different word, from Portuguese achar “to find”, later confused with Spanish echar, but this idiom is very common)
echar un vistazo, e.g. echó un vistazo al coche (“he took a quick look at the car”)
echar mano de (“to make use of / take advantage of / draw upon”)
echar una mano (“to lend a hand”, a false friend of English to throw hands)
echarse a perder, e.g. la comida se ha echado a perder (“the food has gone bad”)
echar a andar (“to get going”)
echar la culpa (“to blame”)

I have incorporated these idioms in my Learning Spanish Words Through Etymology and Mnemonics (2nd ed.).

Google Ngram Viewer may be the best tool to check usage frequency of a word or phrase. You can not only see the current frequency, but also the historical trend. Before this technology, I used to submit each word or phrase (enclosed in double quotes) to Google or other search engines for a search and record the estimated hits. Searching for a hundred phrases one at a time would be very time-consuming. Thanks to Ngram Viewer, the labor is significantly reduced and it only took me about 10 minutes.