Cool trivia moment! That little brush they build into the cap of a mascara tube is called a wand. (OK, maybe it's not really all that cool, but anyway, it helps make sense of the advice I'm about to give here.)
A good trick is to take the wand from one of your old dried up mascara tubes and wash it out. Then if your mascara ever gets clumpy you can take the clean wand and carefully separate your lashes for a nicer look. It's easy and safe because you already have a lot of practice at using that little brush right up close to your poor defenseless eyes.
It's also very important to remove your mascara before you go to sleep, no matter how tired you are. Leaving it on overnight can make your lashes get brittle and break or fall out. You're wearing mascara to make your lashes look better, right? So take a couple of minutes to remove the mascara properly, or eventually it won't be able to help you anymore.