Put in a column near the equation, the meaning of each variable.

Then use differentcolors to highlight each variable (both in the explanation column, and in the equations).

Draw circles/strikes around/on part of equations that make sense by temselves, or represent a concept, or are transformed into other thing in the next step (in a similar way as teacher does in the blackboard while they explain things).

Maybe look for videos explaining the theorems etc (since they visually show all these techniques, I guess).

HTH