There are two types of mockuppers. Which one you want to be?

1. Minderian mockupper

Minderianism uses eye-candy looking bootscreens, but it's unrealistic and as such you can do anything you want with this style.

2. Traditional mockupper

Traditionalism is focused on realism, but at least you can make some screens convincing for some people.

3. Semi-traditionalism

A combination of 1 and 2: traditional look, you can make anything you want.