When writing very long sentences, it isn't uncommon to be burdened by the sheer length of it. More than the mere volume of letters and words, many long sentences end up delaying things that the reader may need to know.
Once you find one of your sentences running a bit too long, try reading it and see if it suffers from one of the maladies below. Make sure to try running it through an English writing software as well and see what it can do to help.
1. Too many words between the subject and the verb.
The most common problem with long sentences is when too many words come between the subject and the verb, the two main anchor points that hold a statement together. If the essence of the actor-action relationship begins to get lost because of so much separation, either writer the sentence to bring them closer or turn them into two sentences instead.
2. Too much description.
When describing an object, try keeping the clauses to a maximum of three per sentence. Any longer and you risk droning on and on.
3. Too many extraneous facts.
While laying the groundwork for the actors on a sentence is important, adding too many facts not directly related to the statement can end up watering down its impact.
4. Too much asides.
While parenthetical asides can effectively be used to offer up opinions and alternate points of view, some writers (especially those trying to be witty) can end up doing it too much. Simply cut it down and save the rest of the side comments for another day.