Easy Spotting Rare Bills?

Well said.



to the CCF!

As "Steve.." points out, try to get special serial numbers in high grade (UNC) would be your "best bet" for finding something "collectible." But it will be quite challenging to try & attain collectible banknotes from circulation. Usually, one has to turn to online sales at some point (& if I do I may buy multiples to keep costs down).

Another rule of thumb I would go by is to keep your ear close to the ground in order to discover what might be a short run or popular. Keep abreast of what blocks (prefixes & suffixes) are less common than others. Educate yourself. I'm just learning about US currency myself so I have regularly checked out this & other forums to learn what is sought after (popular) in comparison to other series/denominations.

Buy less & put the money towards UNC even as you go for older series (go for quality over quantity). If you buy TPG than make sure you get EPQ or PPQ. Consecutive serial numbers is usually a gimmick (for most modern stuff).

While I'm learning there's still a few "no-no's" I abide:
a) I won't listen to or follow what the "experts" from SM (youtube, Reddit, FB Groups) recommend (most of these guys are "armchair" collectors)- stick to forums where guys will disagree with you (SM can be great to learn about a nation's designs/central banks- general info, but that's about it)
b) I won't buy circulated banknotes from SM or sellers I don't know (who don't have high feedback ratings) or a decent reputation
c) won't buy uncut sheets, specimens or banknotes in presentation folders (buy the note /not the folder)

Whether coins or banknotes, collecting from circulation is almost always about "interesting" and not "valuable." I've personally never gotten a BU Morgan dollar in change at a restaurant, so you've got to keep those same expectations in check with banknotes. If however, you wanted to collect a modern notes from every district, then that's certainly something you could work on, especially if you aren't fixated on getting uncirculated notes.
Also, while I know some people don't mind spending hundreds of hours looking through boxes of cents to find a handful worth a few dollars, I'm not sure how many people get $10,000 in 1-dollar bills to go through on a regular basis. If you find fancy serial numbers or star notes from limited runs, definitely pull them out. Personally, the closest thing I've found to "valuable" in circulation was a 1957 $1 silver certificate--worth approximately $2.
I do pull out uncirculated notes occasionally to have an example, but not expecting they will ever increase in value. Inflation obviously lowers the value in real terms over time. Of course, the same can be said for banknotes pulled out of circulation a hundred years ago. Those notes didn't start off being worth more than face value.