There are different schools of thought on this.
I heard once that in visualizing that it's important to be realistic in what you are trying to achieve. If you make $20,000 a year, instead of visualizing a millionaire lifestyle, try starting with perhaps a $80,000 a year lifestyle. Put your focus on that and know that it's a realistic goal. Once that is achieved you will be in a better position to manifest the next level, perhaps $250,000, then $500,000, then $1,000,000.
I, however, think it's important for you to be super excited about what you visualize. After all, it's about the energy that you send out, not the actual number you have in your head. If $1,000,000 gets you all jazzed up, that's the ultimate goal. You are going to be sending out a stronger energy. $80,000 would be great, don't get me wrong, but it's 'sensible', and for some reason 'sensible' doesn't get me as excited.
Of course there's the flip side. If you visualize TOO big, that might sabotage you're whole belief in the process. If you're goal is to be the first man on mars, or fly like superman.... you can visualize all you want, but you might be setting yourself up for disappointment
They say, shoot for the moon, if you end up only getting halfway there, then that's still pretty good. What do you think?