Self-editing is challenging, as it is difficult to gain the necessary perspective from your work to be “objective.” Or at the very least clear-eyed enough to spot those niggly errors that we so often find AFTER we push the publish/send button.
I used Grammarly – which is quite useful in picking up contextual spelling errors, and its grammar check is quite good. If you subscribe to the service, it does have a broader range of “document types” like short-story, or article – which narrows the focus of its checks to be specific to those types of document. You can find more information here: https://www.grammarly.com/
I do also like the idea of printing something out to work on a hard copy – but when this isn’t practical, I save the file as a PDF, and open it in that format. It must do something cognitively because when it is not able to be edited on the fly, and I’m forced to see the work as a whole thing, errors sometimes jump out.
I do also find doing things like changing the font when I re-read something changes the way my eyes skim over lines that I might know quite well. Changing the font forces my re-read to be slower – especially with a slightly difficult to read font. I think this might be best for shorter pieces though – or sections.
As others have suggested – I find examining each word in a reverse order useful for finding spelling errors. But it is time-consuming and can be fatiguing on a longer piece of writing. I find this less helpful for grammar. Reading out loud helps find those difficult sentences.
The main thing I do to condition my self-editing reflex though is to read lots of other things and try and notice the things I would change if it were that my piece of writing – and thinking about why I would do that. This helps me to figure out what is unique to my voice and also trains me to notice the things that jar me when reading. Hopefully, that means I can see those things when writing for others as well.
I hope that’s helpful!