Minimal pair activities are a good starting point.  Attached is an example of a minimal pair activity that I do with my grade 3 elementary students.  Its a logic tree, you make 6 sounds (or words) and then ask the students to select the final word.  You start out with really simple phonemes that are similar to each other.  In my example, the goal of the lesson was to practice the /p/ phonemene, so I decided to pair off /p/ vs /b/.  You can google "minimal pairs X" and change X to whatever you want to practice to get all the words to fill out the chart.

I like to it out as a listening activity.  Phase 1, the class practices the /p/ and /b/ sounds in unison. Phase 2, the teacher travels down the simple /p/ vs /b/ tree (students echo).  Phase 3, the teacher travels down the minimal pair /p/ vs /b/ tree (students echo).  Phase 4, student volunteers travel down the simple /p/ vs /b/ tree.  Phase 5, student volunteers travel down the minimal pair /p/ vs /b/ tree. Phase 6, the students organize into pairs and practice the tree most appropriate for their ability level.

The end result are flowers because that's the vocabulary I wanted to practice that day.  For middle school boys you could easily change them to either video game or Kpop characters.

The point is, use something familiar to help them remember the boring letter combinations so that they are more engaged, will progress faster, and less likely to forget.

I agree. BTeacher has some good ideas!

When I want to practice pronunciation, I put the words they are learning on the board, along with some words that sound similar. I write them all over. Then I give them a sticky ball and they have to throw it at the word I say. If it hits it, they get two points. This is a good team game too. Everyone loves throwing things! Haha!