Still, it can be done, if the writer takes at least a few weeks off to get a bit of distance from the story.
Once that's done, the writer needs to do two things.
Firstly a fast read through of the story. Reading through your work in as close to a single sitting as possible will hopefully show you where there are lulls in the story that nearly grinds its progress to a halt. Or conversely, where things are happening on top of each other so fast that the reader won't be able to catch up.
If the pace is too slow, either shorten the period before the next big event, or work something exciting into the lull. If it's too fast, you might want to look into bridging scenes. These are slower scenes designed to give the characters and the readers a chance to rest before the next thing happens. It gives them all the opportunity to think of the events just past before the next one. If those scenes aren't there, the story won't have an impact on the readers, because they won't have a chance to sink in.
The second thing that a writer needs to do is an out-loud reading of the manuscript. This is to catch the tiny things that hurt the flow. Words that repeat, sentences always of exact same length, or similar sentence structures repeating too close to each other. Same goes for paragraphs. Think I'm being nit-picky? Try this:
Inspecting the room, he walked in. People stopped talking and started staring. Pausing for a moment, he frowned. Why were they staring like that?
Doesn't feel nice to read, does it?
He walked into the room, careful to look relaxed while he inspected its occupants. Silence fell as he made his way to the bar. Frowning, he ordered a drink and took a sip. Why were they staring?
Still not the best lines ever, but lots better than before. So when you read out loud and things feel weird, look for repetitions and change them up.
Flow issues take a bit of effort to spot but once you know about them, they're among the most clear-cut issues to fix. Only one more thing: The fast read is best done during revisions while you're making big changes to the story. The loud read works best right at the end when you only need to change wording and such.
Look Out for These:
1) Long periods of unending action or no action.
2) Something sounding or feeling off when reading. Few people can catch structure repetition, so if you can't put a finger on what's wrong, go looking for repetitions.
3) Crit partners or betas pointing out the above. LISTEN to them. Odds are they'll catch flow issues much better than you will.
What do you do to catch flow issues while editing? Are you one of the lucky few with a natural feel for flow, or do you have to go looking for the problem?