Clients often send me a contract, do I send them mine too?

You only need to sign one agreement with your client, so if are comfortable with the terms in your client’s agreement that would be sufficient. Otherwise, you need to negotiate the terms in one of the agreements. You cannot have two agreements in place at once. If you are uncomfortable with what a client is asking you to change in your agreement you should always seek professional advice from a lawyer or solicitor if you are based in the UK.