For one thing, the task of invoicing is much simpler if you have basic spreadsheet skills. Some clients request invoices on spreadsheets, and it makes sense because it takes care of all the adding up for you. I've had clients who have sent me assignments in spreadsheet form, with different columns for things like contact information and links I should use. I don't pretend to be an expert on Google Spreadsheets or Microsoft Excel, but I have enough basic skills that when I need to use a spreadsheet for invoicing, organizing sources, or taking care of an assignment at the request of a client, I can handle it without the process costing me half a day figuring stuff out.
Same is true for word processing software. Sometimes clients want documents put in pre-made templates. If you're asked to write an eBook, for example, you may be asked to use a template provided to you. In these cases, having some knowledge about formatting techniques for Microsoft Word (the most commonly-used type of template I've been assigned) can really help.
My sore spot is usually Microsoft PowerPoint. Back when I worked in an actual office, it was in the days before PowerPoint, so I never really learned how to use it. But I've had to cobble together enough PowerPoint skills that I can use it if a client needs a product in that format.
Another skill you may be asked to use (and one you should include on your profiles on freelance sites if you have it) is experience in posting to blogs using WordPress. Many, many clients use WordPress to power their blogs, and the more you know about getting stuff uploaded and formatted correctly, the better. Some clients may ask you to do some basic SEO when you upload to WordPress, and this is also a great skill to have (and advertise).
OK, so how do you go about getting these skills? If there's a community college in your area, check their continuing ed courses, because sometimes they're offered either on the entire Microsoft Office suite, or on the various programs that make up Microsoft Office. If that's not an option, Microsoft offers a wealth of resources for training on all the Office products, and they're free. If you have a slow work day, this can be a good way to use your time.
Microsoft also offers a large number of free eBooks for training that you can download to your computer, Kindle, or other device that make good references, or that you can work your way through as you have the time.
If you're new to WordPress blogging and a client asks you to upload content to their WordPress blog, here is a good video to help you get the basics. If you have the basics of WordPress down and want to learn more advanced skills, try this site. You can learn the basics about the All in One SEO Pack Plugin for Wordpress with this video tutorial.
As a freelancer, you may never set foot in a traditional office, but having a solid grounding in the software used by your clients is a tremendous advantage. You can advertise these skills on your freelance profiles and resumes, and let clients know that when they hire you to write, you're going to make things as easy as possible for them.
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