You can use makeup to make your skintone paler, but if you go too light or use too much it ends up looking really fake. A good rule is to not go more than two shades paler than your normal skintone. If you do this, make sure that you cover thoroughly (don't forget your ears, neck, etc.) and blend everything really well.
One thing that can help with blonde characters is to pick a shade of blonde that works well with your skintone. I've got olive skin with yellow undertones, so certain shades of blonde make me look jaundiced. If I'm cosplaying a character whose hair is that shade, I'll try to go for something close to that color, but that works better with my skin. It wouldn't be exact to a reference picture, but the end result is a LOT more natural-looking.