How to maintain the motivation
Firstly, you have to decide a purpose that should be clear, specified and it shouldn´t take long time. You can imagine enjoying your objective. For example, if the purpose is speaking English, you can represent an image of yourself speaking fluency with natives or writing an English book. If you can see the image associated, in first person, maybe the feelings are bigger. You also can make the image bigger or change the colour to make it better to have more feelings.
All those emotions will increase the Dopamine in your body, therefore you get a satisfaction feeling. But if you want to maintain the motivation, you also have to fix several purpose during the process to get a little level of Dopamine to rewarding you and feel satisfaction.
The neurotransmisor Serotonina has an important role regarding the pleasure, the mood, survival motivation... So, make sure you have means to stimulate the production of that.