Check Free Space on Emulator - adb shell
Your Android Emulator must be running for this to work.
Open a Windows Command Prompt / Mac Terminal.
Go to the directory of the adb.exe program. (Not necessary if you have this in your PATH.)
On Windows (example location):
cd c:\Android\Sdk\platform-tools\
If you only have one running emulator, you don't need to specify which to connect via adb shell, so just run:
adb shell
If you have multiple emulators, you can specify which one after finding the name using
adb devices shows running emulators

Connect to the emulator
adb -s emulator-5554 shell
You'll be presented with a shell prompt inside emulator:

You'll have limited permissions, so switch user to root with command:
su
Use the disk filesystem command to see disk usage & available space
df

If you're running out of space, the Use% on /data will be high. You need to free up space on /data
Free up space by deleting apps you've installed...
Delete Apps in adb shell
Your apps are found in /data/data:
cd /data/data
It's easier to see your apps by reversing the directory listing sort order so your apps will show at bottom:
ls -ltr

You can delete your app directly here using rm -r. In the above example the app is stored under com.mobdev.user_interface_intro:
rm -r /data/data/com.mobdev.user_interface_intro
Repeat for any other apps you want to delete from the emulator to free up space.
Delete App in Emulator
You can also delete the app within the running emulator itself. Click on the Square button > Android Settings (Gear Icon)

Click on Apps & Notifications

Find and click on your app

Click on Uninstall

Repeat as necessary for other apps you want to uninstall to free up emulator space.