Import from IMDb

1. Open your ratings history and watchlist pages
2. Click Export on both
The button is near the top.
3. Open your Exports page
Just refresh if they're not ready yet. You might have to wait a couple of minutes.
4. Download both files
by clicking Ready. They will have names like 8aecc553-dbbe-41af-8e0a-54076de7814e.csv, but the order isn't important here.
5. Upload them here
and check the results
Done? Check your profile and watchlist