Now onto this first entry...
I dare say that the #1 problem that I see in stage makeup is not having enough on. You need way more than you would for an everyday look to be visible on stage. There are multiple factors that are contributing to this.
Just by the sheer fact that there is some distance between you and the audience (generally a good 5-10 feet at a minimum), you will need to have more makeup on to have it seen.
- Bright lights
If there are actual stage lights, then they will make your face look instantly several shades whiter than you normally are and it's like your makeup has just washed away/vanished. So, again, you'll need to have more.
- Dim lights
Dim lights are the opposite effect in the sense that it will make everything appear darker... but, again, if you're barely wearing anything, you'll just look like you're wearing nothing.
I love to joke that you need to look utterly unnatural to look natural on stage and in pictures. For all that I say it jokingly, it actually is very true.
So, when you're wondering whether you have enough makeup on your face, chances are, it's not enough. One tricky thing is that, when you're putting on your makeup, you'll be very close to the mirror and, therefore, it will seem strikingly excessive... If you've reached that point, then you probably have just about enough... or maybe you could have more. It all depends on what you're used to. Most people wear very little to no makeup on a regular basis... so if I'm asking you to put on makeup like you're a drag queen, of course, it will feel ridiculous and like it's way over the top. But that's what you need to look polished on stage. Seriously.
I've had people laugh at me when they see me apply makeup on a friend and I'll pull away a good 5 feet before deciding whether I need to apply more or not (and whether it's even or not). I know, it looks like I'm an artist painter... but, really, it's the same thing: that painting won't be seen from nearly as close as the painter is... same with the makeup. What you can do yourself (and I do that a lot) is pull away from the mirror by at least 5 feet and see what it looks like. You'll be surprised at how quickly the makeup that you thought was good ends up vanishing. So do make sure to do that "silly" step as it will be a good indicator of what it will look like on stage.
Now the cool thing about distance and lights and all is that it will hide a host of sins... so if, while you're close to the mirror, you think that you've messed up grandly and the makeup is uneven, look at yourself from 5 feet back... it's probably fine. If not, you'll likely not need to correct the makeup by nearly as much as you'd think. ;)