A good way to start is to download templates from the Microsoft website. They will allow you to modify their templates according to your preferences, but they'll also offer an easy way to make your own. Using Microsoft Word, you can make your own label templates, quick and easy. If you look at the top and on the edge, you'll see some measurements. Those measurements will help you gauge the location of the label parts. Move them around and try them out, change fonts or locations, add pictures and so on, and once the label looks like you want it, click File, Save As and select Word Template. Under File Name you can give it the name you want. Click Save to save your modifications. It's as simple as that. You can create as many templates as you want, and all of them will be stored in Open Office documents.
Personally I like to place my business address at the bottom of the page or the footer. To do this go to the floating bar and click on the button, 'Switch Between Header and Footer.' This will open a dotted box at the bottom of the document. You can type your office address here or anything you see fit for your letterhead. Again you can format the text by choosing the font, font size, color, align the text, etc.