You have your location, composition, and modeling skills all ready, but how do you actually take the photo? There is absolutely no right or wrong way to do it and in some cases you may have to get really creative. (I had a classmate in art school who taped his DLSR to the ceiling with duct tape - I do not recommend that) I suggest starting with these three options: tripod, human tripod aka friend/sibling/life partner volunteer, or handheld.
When you take self portraits, prioritize safety by not placing your camera on risky platforms. Use a tripod to keep your camera in a consistent and safe position. Once you have your camera facing where you want it to be, it can be tricky to gain focus on you while you are behind the lens playing with settings. Put something in your composition where you will be posing. Focusing on this object will help the camera focus on you when you trade spots. Height of the object is not as important as distance, but try to match it to yourself as best as you can for accuracy.
You can also try focusing with a remote or autofocus while you are in front of the frame. This may take a few tries, but once it is established it can save you time an energy of getting up, focusing, and going back to position.
If you do not have a remote, try using the timer and burst mode on your camera. This will at least give you time between your pose and pressing the shutter. The burst mode will give you multiple options in one sitting (so you can guarantee your eyes will be open!)
If you decide you want to handhold your camera to take your photo, remember that your distance between you and the lens is relied solely upon the length of your arm. Naturally, you may also shake which could result in blurry images. On the other hand, this may be the exact kind of framing and effect you are seeking.
You are not cheating if someone assists in taking the photo for you, but use them only as a human tripod and remote. You still need to have full control of the image and how it is taken. Set everything up and direct your human tripod to stand and focus where you want.
Take Your Time:
You may not be a professional model, so getting into a pose and finding what feels/looks good to you may take some time. Self portraits are filled with infinite possibilities, but has some limitations. It is exhausting. When losing energy, you’ll feel very impatient, irritated, and uncreative. Take breaks, have snacks, listen to your favorite music, and treat yourself like you would your best model. Are you getting discouraged? Call it a day and try again later.