Isn't this the most annoying answer?
“A blog post needs to be as long as it it needs to be. “
It is the best advice I can give and it will only take a short blog post to support my point ;)
Don't keep it short just to limit yourself.
If the point you're making is simple, you don't need to strive towards a particular word count – just make your point and engage your audience well.
Check out how Seth Godin never uses more words than he really needs to to make a point.
If you're making a complex point, you shouldn't try to limit your word count to ‘keep it short'. You'll just frustrate your reader by leaving them without full understanding.
Think about some of the blog posts you've really loved reading. I'm sure they are of varied lengths – just the right amount of words to make the desired impact, right?
See how Derek Halpern goes deep to prove his points.
Don't go long just to make it seem more impressive.
I am for ‘writing tight' when it's possible. Keep the adjectives to a minimum and don't repeat your points in different ways. That's filler.
Don't veer off left and right with a lot of ‘oh by the way' stuff. You don't need to support every thought with a story. When someone does that I get bored and end up clicking away.
Engage me! Know what you want to tell me and deliver it in a clear personable way.
If you do that, I'll enjoy your post, whether it's 230 words or 2300.