Anything that increases overall health will help
asthma - exercise (once you get the exercise
asthma under control - may involve taking a puff or two of ventolin before you start), eating healthy - limiting sugar, caffeine, alcohol, fatty foods and increasing vegetables, fruits, lean meat, healthy fats and whole grains. Staying hydrated with water is also very important for asthmatics.
Identifying and eliminating your triggers are important - you said exercise or laughing/sneezing.