You just don't charge your clients without considering some factors. If you do, you may not have more clients to patronize you. Some of the factors will jncnzhe the nature of the gig. For instance, if you want to write articles for clients, you need to consider the topic, how complex is it? Then consider the duration of the gig and even the number of pages of the articles. All these need to be considered before you decide how much you need to charge the clients.