Using your cell phone, of course...
1. Try a selfie stick (check out link to article for brands they recommend)
2. Be aware of the lighting in the image, try for lighting that is indirect, lighting your face. Even if it’s to the side, it’s usially better than having the light directly behind you.
3. If it’s a group shot, either have the person with the longest reach shoot the pic, or use the timer that is built into most smart phones and set the phone on a safe, stable surfice.
If possible, I always try to enlist the help of another person for group shots ~ ALWAYS check the quality of the pics tho, you never want to assume they turned out and then miss a shot of you with your crew...
Cheers and Happy New Year!