I believe anyone who has traded seriously and never made a "dumb" mistake is a liar.
That is why "to err is human" has survived so long.
My experience has shown me that probably (never kept records) 90% of my mistakes occurred when I was rushing to catch a price. But, experience has taught me to relax and enjoy my trading time. If I miss the exact price (not often) I simply decide if it is worth the greater risk and smaller profit target, if so I go anyway.
When I was still trading on my own, I did my best to set things up so as to minimize mistakes. I use the Best trading platform (not most popular) because it offers ease of order entry and control, while not being as complex a setup as J Trader for example. I keep three separate "quick trade" windows: market, stop, and limit in positions that help me avoid sending an incorrect order. And the buy and sell buttons are clearly green and red.
I also use alerts and a timer to keep me on track, as I learned that "watching" the screen too much caused me to over trade.
After doing as much as I could to reduce my mistakes, I find it is best to put more attention on what I do right and accept that the rest of it is part of the package. Just as losing trades are part of making money daytrading!