A handful of times a year, a decently liquid quasi arb appears on just my scans so there are probably a ton of "no brainers" out there. If you learn to price something very well (stocks, vol, real estate, credit, etc..) and price many assets, comparatively and in absolute terms, you'll likely find some wild mis-pricings every year - especially in the less liquid stuff. The caveat is, the less liquid something is the worse the data is so it makes it harder to build a good scan.
I may not be the best to answer as one of the things I'm adressing is increasing my trade quality by reducing my trading frequency. Obviously, the best directional trades are the ones where you will: a) Lose very little if you're wrong (which you will be) b) You're executing at a spot where you can reasonably risk very little with a good chance of not being stopped out c) You can reasonably expect to make considerably more than you risk A real life example would be when the market is moving higher and you have reason to expect that a larger move higher is on the table. You go long on a pullback to a key level. If you're wrong, you won't lose much. If you're right, you will get paid substantially relative to your initial risk. A real life example of a bad trade could be that very same move, except you missed the early entry and you're now doing a chase entry say 10-15 points away from where one may expect the move to top out and you're executing late in the session. Sure, there may be 15 points on the table, but you're at a vulnerable spot as the market may now first do a deep pullback before finalizing the move. The risk/reward just ain't there. Maybe I didn't quite answer the OP as what makes a trade a no brainer would be conviction based on your own methodology, understanding and experience trading a market. For some, that may be some kind of secret sauce they don't want to share.
James B. Rogers, Jr. is a great role model on the subject. From Market Wizards: His entire interview is really great. He's a fundamental trader who doesn't even use charts, but top, top stuff for anyone playing this game.
I definitely agree that sitting most of the time is the best strategy. The best rewards to risk (no brainer) trades only show up once in a while. I missed the rally in the indexes and didn't trade much for the last month. Now I should be looking for the next trade. Either shorting this bear market rally or longing the next bull market reaction. The Q is ... are we in a bull or a bear market ?
And the answer is often not what they want to hear: Study the setup. Find a way to search for it in other stocks. (write a script for a search) Filter out the lowest probability setup (low volume, low price, biotech, ETFs, ADRs) get your allocations setup so you don't over or under buy for your available funds. Setup your entry orders in tranches. Get an entry, watch to see if you need to buy more or abort. Find your exit based on signals, price, or whatever was in the setup you are targeting. In other words, Do your work, stop the FOMO, stop the pontificating, stop the posturing etc. Trading is like any other endeavor, preparation has to meet opportunity. It is not about being right, or making big scores, or finding some Grail. It is about doing the nuts and bolts of trading. After you do that, and you have time, then you can start screwing around if you want.