Have any tips on using various Media in my story?

Facebook's image guideline:

• Image ratio is 1.91:1

Kik's video guidelines:

• Videos are limited to 2.5 minutes in length and must be under 15MB.
• Videos to be autoplayed in the client must be under 1MB.
• Try to use only mp4 videos.

Editing Stock Photos

Stock photos are nice, but they can look, well... like stock photos.

You might want to crop a picture to focus in on what you need. Rotate it slightly so it looks more casual. Blur it a bit, so it's not so crisp. Maybe add a visual effect, filter or tint that makes all of your story images look cohesive. I.e.: the photos were all taken from the same phone camera, or all the images evoke your desired tone and mood.

Original Image:

Edited Image:

Using Gifs and Movs

Employing animated/moving images can have a big, positive impact on engaging your reader. They are usually delightfully unexpected and can be a great way to "break up" a long string of static photos.

Using YouTube Videos

You can link out to a YouTube video, but take into account the length of the video segment. You might not want to link to a long, extended video and risk "losing" the engagement of your reader.

Please see more detailed info in the YouTube FAQs.