Use best practices that ensure proper rendering and display.
A gif is a series of images saved as one image file. Every frame takes up the same number of KB as a normal image. Beyond 15 frames, the gif may be too large for some inboxes.
Create the final frame or step in your gif to display the most relevant information, and set it to remain longer than the other frames.
For example, if you create a gif that eventually displays a 20% discount offer, set your final frame to stick for at least 10 seconds on that offer. Users will rarely wait for a gif to reload and start again, so if your discount offer only appears for 2 seconds, it will probably be missed.
This allows time for a user to scroll down to the gif once they open the email.
For example, do not show a flashing discount offer pop-up and have a CTA button change color at the same time. This will overwhelm the user and reduce clicks.
If your image size is larger than this, your email will not render correctly.
For example, if your gif is promoting a 2 for 1 offer, mention this in the text as well. Some inboxes will not render gifs and a user could miss out on an offer.
Your email marketing platform will usually treat animated gifs the same as still images.
Concisely outline what was contained in the gif, particularly important information like 20% off offer with code 20SALE. You do not need to describe the image visually if an offer is the key takeaway.