How do you face the situation where you want to write but cannot find the words or do not know what to write (also known as writer's block)?

Easy!  If you only write the truth, and not fiction, you will never have writer's block.

1. Try new methods, tools or software.

Changing your medium of writing would bring in new ideas and challenges. Switch from longhand to computer, or from computer to long hand to get rid of the writer's block.

2. Write something completely different.

Try your hand at writing something that is completely different from yours typical slight. That could freshen up your mind and boost your creativity, too.

3. Give yourself a prize!

Giving yourself an incentive works. If you resolve to give yourself2 hours at a movie theatre after completing a piece of writing.....that should organised you better. Likewise, think of your own predilections and culinary preferences......and promise yourself to indulge in them after completing an assignment. This would surely help.

4. Try a change of scenery.

Changing your place of work should re-energise you and help move from a stuck-in-the-groove position by providing a newer desk, a better room and a window that opens on green grass!

5. Just get on with it.

Don't give up if you are stuck! Force yourself to write. Concentrate. Keep pushing yourself. Don't give up. Persistence would pay!

I think each one of us has her/his own way. Try to relax and don't think too much about it. Give yourself a break like you can go for a walk or watch a movie. This is what I do exactly: take a break, stop thinking and worrying for some time. Go back to my writing and do some brainstorming then write anyway. Ideas will flow without noticing. Get involved in your writing and don't feel stressed. 

I try to read and listen to music hoping to get inspiration from it, or I give myself a break until I feel like writing again.