I do not suggest you try to have triplets on purpose
I do not suggest you do anything to try to increase your chances of having triplets. Multiples pregnancies have increase risk of complication and an increased risk of fetal death. Do not try to increase your chances of multiples on your own without your doctors approval.
Many doctors suggest that a mom pregnant with triplets consider selective reduction. If you doctor is giving you fertility treatments they will monitor you closely and discuss the risks of having multiples.
Please do not do anything without your doctors consent. Make sure you are informed of the risks.