Back To The Basics
The first secret of increasing your receiving speed is to shorten the time it takes you to recognize each code character as soon as it has been completely heard. The shorter that time interval is, the faster you will be able to receive. Aim to make it instantaneous. IF YOU DO NOT INSTANTLY RECOGNIZE THE SOUND OF ANY CHARACTER, YOU HAVE NOT REALLY LEARNED IT YET. (That is the one character you need to practice on until you know it immediately.) The goal of practice and drill from here on is to speed up your recognition of characters, and then of words, to the point where you can both "read" them easily without writing, and copy them down more and more automatically.