Some things that were high value to me,

1. Play through the first page of levels of TIS-100. This is a game you can buy on Steam. After spending a few hours working on problems in this, I felt a hard-to-describe mental shift that removed the intimidation of assembly.

2. Work through the first half of /Programming Boot Sector Games/ by Toledo.

3. Designing and building a simple instruction architecture, implementing it as a VM, writing an assembler for it.

The ChibiAkamus tutorials on youtube may be worth a look, also.

If you try for TIS-100, give yourself a decent chance to get into it. Print out the manual, calmly read through it with a biro, don't let yourself give up easily on the first few problems.