I assumed you'd been blonde blonde and wanted to go dark, how old are you? I have dirty blonde hair too and have had it highlighted since i was about 15 to be blonde, i've been just about every shade of blonde possible and a few years ago i went a dark chocolate brown. I notcied a massive difference in people's perceptions of me, and had people telling me whether they liked it or not without even asking them! It's a big change if you're very blonde, i would suggest talking to the hairdressr explain that you want to go brown - but say how brown ie penelope cruz brown or kate beckinsale brown, then i'm sure they'll be able to suggest it, they're trained to look at tones and skin colour and should be able t help - have fun with it though, it's only hair and you can always lighten it again!