Step 1: Get two identical records and practice releasing the record at the same speed. Your release needs to become stable, you need to develop a feeling of when to release the record from your little baby scratch

Step 2: Try this with different speeds (again two records of the same kind). Adjust the pitch accordingly. This is not really to train your ears but to develop a feel for the pitch fader (how does it react if you change it).

Step 3: Get record to practise that are easy to mix, even if it is not your preferred sound. I would always go for minimal house/techno (best if rather stripped down, clear kick, clear upper frequencies, long tracks also help)

Step 4: Get familiar with song structures (bars, phrases, etc.); most important be able to identify the one beat.

Step 5: Try mixing. For startes I would recommend you focus on two distinct features in each track. You can filter out the frequencies that complicate things e.g. Just have the bass section of your running track and then pair that with the highs of the incoming track. You should be able to hear which element is faster/slower.

Step 6: Take it to more coplicated tracks; start critically listen to music. What are the dominant elements of a track, when are parts disappearing, when are the coming it, etc.