Fashionistas, I need your advice !!

Finding out about a black tie event a week beforehand = nightmare! What am I going to wear ??

One week is not nearly long enough to plan, re-plan and re re-plan an outfit. Although I am finding that I am getting better and better at this. There is an assortment of outfits and you can never go wrong if the following ground rules are followed (keep in mind I work in a conservative, male oriented industry):

• Work related (entertaining clients) - keep it conservative. Limit display of leg and cleavage. Afterall, you don't want any of your clients thinking they'll be getting more than the goody bag!!
• Work related (where you have been invited) - can be more riske. A bit of cleavage and leg never hurt anyone, plus you can spend the night enjoying yourself and chatting to people you actually want to speak to. Again though, aim to go home with just the goody bag or if feeling adventurous the table flower arrangement ;-)
• Any not fitting into the above - its time for that low cut number you never thought you would get to wear! Worries are out the window ... you are a princess for a night! Just make sure your prince doesn't turn into a frog

Now I have decided on the dress - a black strappy knee length Karen Millen number - the question is can I pull off a pair of flats - Marc Jacobs ballerinas? I am 5'11''

HELP!!