The b d confusion is something that every new reader goes through. Some go through the adjustment quicker than others and some readers may have some developmental or visual issues that really make these letters a challenge.
When I introduce this lesson, I ask the kiddos what sound they hear at the beginning of "baseball" and "drum".
Then I ask them to imagine that they are stepping up to the plate as a batter. We even stand up and act it out.
I ask them what they need 1st in order to be ready to hit the ball. Sometimes the response is "a ball". This is great, so we have 2 students come up and act out a batter with a ball thrown to them...without a bat. A wrong answer actually works great here! They laugh and then correct the answer.
We then draw the lower case b and say,
"First the bat: Then the ball"
Next we imagine playing the drums. What does a drummer need first?
"First the drum: Then the sticks"
Draw the drum and sticks.
Then have students hold up their thumb hands facing each other. Trace the left thumb down, saying 1st the bat. Trace the remaining fingers in a circular motion, saying, Then the ball.
Trace the right fingers in a circular motion, saying, 1st the drum. Trace the thumb down, saying Then the sticks.
Of course we also put those thumb hands together to make a bed. Point out the b as the first sound in bed, and the d as the ending sound in bed.
I always show them all the tricks, you never know which one will be the best trick for them!
Another one is that lower case b is inside of a capital B.
Lower case d is backwards from the capital D.
Whatever works! :)