Attention spans are short, especially today. Some might blame social media, but the proliferation of online content is likely the greater cause. With so much content out there, writers can't afford to go on and on. Readers expect clear value, delivered fast.
No matter what you're writing, it's often best to keep sentences as short as possible. Fewer than 25 words is a fine rule of thumb. If you need to go higher, have a very good reason for doing so. Remember that shorter sentences tend to propel readers through the text at a quicker rate, while longer ones act as glue for readers' attention.
That said, don't forget to vary your sentence length. Yes, most should be on the shorter side, but don't forget to include long sentences when appropriate. All short sentences might. End up. Sounding. Kind of. Awkward.
For example, while Charles Dickens may have reveled in the long sentence and subordinate clause, this makes his writing less accessible now than it should be. That's a shame.
Note, however, that Dickens was also a fan of the short sentence. For example, the opening of Bleak House reads like this: "London. Michaelmas term lately over, and the Lord Chancellor sitting in Lincoln's Inn Hall. Implacable November weather." Here Dickens uses short sentences to great effect.
Err toward the short sentence, but strive for a good balance. Use our writing improvement software to find places where your sentences might've stretched too long.
Your next writing improvement tip: Improve Your Writing Tip #16: No wasted words.