Whatever your niche or business revolves around if you do work for clients either in the same country or international one of the best ways especially if you are based in the UK is to use PayPal as your form of payments.

Paypal charge low fees for sending and receiving money in your account which is fantastic when you need to bill international clients. You can also build your own HTML forms and have it linked to your account which means you can direct your clients to a page on your site for example www.domain.com/pay-invoice.html where your client may input their invoice number and pay either with their own PayPal account or even by a selection of credit/debit cards which they support.