Your avatar appears to the left of all your tweets, so it's your official face on Twitter. People don't like following you on Twitter if your avatar is just the default. So make sure that you change your Twitter avatar to a photo of yourself or a picture of something else. You can also change your Twitter avatar as often as you like.
Some Twitter users change their avatars almost daily to different photos of themselves, while some users leave their avatars the same all the time, and still others change their avatars according to a specific occasion — holiday-themed photos for Christmas or Halloween, for example.
To change your avatar, follow these steps:
Sign in to Twitter, click your username in the upper-right, and choose Settings.
The Settings page opens.
Click the Profile tab.
Filling in profile information helps people find you easily.
Click the Browse button and navigate to the picture that you want to upload.
Twitter supports the .jpg, .png, and .gif (including animated .gifs) file formats.
Click the Save button.
Your picture is uploaded to Twitter.
The size of your profile image is restricted to 700 KB (which is a rather large image), and Twitter crops it automatically into a square for your public profile. Choose an image that's square or close to square, or make sure that the part of the image you want featured in your avatar's thumbnail version is in the center of the image.
Try to find a picture that's at least 73 x 73 pixels. Otherwise, Twitter stretches the picture out, causing some distortion.
If you upload a photo and it doesn't look quite right, don't panic! Just find a new picture (or adjust the original file) and try uploading it again. You can upload a new picture at any time.