Alpha men usually tend to have their hair cut tight to their head. You will rarely ever get any alpha male vibes from a man who has bushy and rough hair. Though it is possible but it is rare. Hence, you can easily look more alpha simply by getting your hair cut shorter.
You may not like it at first in case you are a fan of lengthier hair, but you may get used to it with time. Apart from that, wear clothing that is well-fit and tailored according to your measurements. This might perhaps be one of the most important factors!