Everyone, it seems, has an opinion and a pattern. Check out craftpassion and 1 Million Masks. Here's one with lots of explanation of why this is best by a retired medical professional. Even Jenny Doan has a tutorial. Some are safer than others. Coffee filters and paper towels do not provide protection from this virus. Two layers of high-quality cotton and iron-on interfacing may be good enough for you, but probably not protective enough for front-line health care workers.
Let us know if you have other favorites and what you do with your masks.
*****It's important to communicate with the recipient of your mask project before you make them. Each hospital/Dr office/nursing home/rehab center etc has its own specifications which may or may not conform to the CDC requirements.