What zone are you growing in?
Mandevilla are hardy in zones 9 - 11.
The plants will not survive in a colder zone and should be brought indoors when temperatures drop below 50 degrees F.
In warmer climates the plant will generally can be trimmed back in the winter about 6 weeks before the last frost. This will help produce a nice bushy plant.
Trimming of the vine all summer can help keep it in control.
Every 2 to 3 years you can trim the plant back to the ground to reinvigorate the plant.
If you are in zone 8 or colder, your plant may not have survived.
If you are in zone 9 or warmer, you plant should began to grow when the weather warms.