Three stretches worth trying are:-
Stand on your toes on the edge of a step. Drop your heels down below the level of the step and hold. Bring yourself back up and repeat. Do the exercise slowly and don't bounce up and down. Don't go beyond feeling a stretch - no pain!!
Stand a few feet out from, and facing, a wall. Lean to the wall and take your weight on your arms. Keep your feet flat, with one foot closer to the wall than the other, then drop the back knee down and feel a stretch. Repeat a few times each side. Same precautions as before.
Sit on the floor, legs together. Lean forward at the waist and grab your toes. Keep your legs flat to the floor and pull your toes back a little and feel a stretch in the calf/achilles region. Same precautions as before.
If the achilles is always stiff putting a heel-lift in your shoes may also help.
I should add that I am not an expert, however, I find these exercises etc useful.
Good luck.