I used to work for them. Here are a few tips:
1) Ask them to demonstrate everything they are offering you. In many of their sites, the internet service is quite poor. Ask them to test the speed. Ensure that no website are restricted on your internet connection.
2) Ask them to demonstrate to you their telephone system. Ensure you see how they will answer your calls & how your phone works. You will have to pay for at least 1 telephone line. Ask then to confirm in writing the best call rates. It costs extra to get an itemised copy of your phone bill. See if you can get them to include this in the negotiation process.
3) There is typically a beverage fee that is non negotiable. Along with a 1 or 2 month bond that is non negotiable. In many cases, see all the online tweets etc, they do not refund the bond, so be prepared to kiss this money goodbye at the end. When you leave, there is a fee to fix up the office. Ensure you get from them in writing what this fee will be when you exit.
4) Ensure that your notice period is only one or two months, to be safe. Give notice when you start in writing so that you don't forget. If you do not give notice your lease will roll over for the original period you signed for.
5) Read the lease, in full. Don't skip any clauses. Get in writing any amendments to the clauses. They do not honour any amendments made verbally. It must be in writing.
I would suggest from experience that you use a broker like www.instantoffices.com or www.officebroker.com. They will generally negotiate a tour for you. Always tour. You can then see what you are getting for your money; no smoke & mirrors.