I've been waiting for the longest time to share these guidelines with other people. If I can do it, so can you.
1. Place hand over door handle/knob
2. Turn handle
3. Pull/push on door to open
If this doesn't work:
Try coaxing the door open by magic. I've seen it work in Disney movies.
If it's your own door, kick at it until it opens. (note: this is not recommended if you have neighbors)
If all else fails, consider the fact that the door may be locked.
Thanks for reading, hope this helped!