Depending on the nature of your business, the sale of your goods or services may be dealt with by standard terms and purchase order. Where a more complex project is involved you will need to negotiate a more bespoke contract.
If you supply IT services things are not so simple and so you must always think about the duration of the deal and develop bespoke IT contracts to help protect your business and its assets. For example, you would aim to negotiate long term notice periods in order to protect good customer relationships. When dealing with specifications as a supplier, you must always think in terms of physical hardware and hours of labour. Avoid IT contracts that are based on outcomes where possible.
Consider who will be the owner of the IP (the Intellectual Property) produced during the course of the contract. If there is no clause in your IT contract expressly dealing with the IP it will, in all likelihood, pass to the customer.
Developing a bespoke IT contract on a client-by-client basis with these considerations in mind will help avoid claims made against your business, and litigation further down the line.