We have tried to maintain our prices over the last [x] years, as we appreciate the need to help your business during these tough economic conditions. However, we are no longer in a position to be able to do this and regrettably will have to increase our fees with effect from [date]. The new charges are as follows:
Price 1 Price 2 etc
Also, to confirm our payment terms, we are a service company and expect payment within 14 days of invoice date.
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Sorry it's a bit lame, but it's a starting point.
On the payment side, you could go for a carrot approach - increase all your prices by 10% and offer 5% discount for prompt payment - or a stick approach - start charging a late payment penalty, although if someone doesn't want to pay, charging them more isn't going to help!
If your work is fairly consistent or fixed fee, you could offer to accept standing orders.
... and, of course, you can also use the Letter of Engagement to set out your payment expectations from the outset (plus mention of any recourse you might consider in the event of not being paid within an acceptable timescale - like stopping work or/and pulling out of the relationship).
I think Nick's highlight that bookkeepers are service providers is also well made. Some clients are happy to delay payment as if we were just supplying goods from stock when, in fact, it's real bread, butter and bills that we are talking about.
