What is your tolerance like to other opioids? Subutex is very potent, and a lot of people get sick due to underestimating its potency.
0.25mg of sublingual subutex is roughly equivalent to 10mg oral morphine to give you an idea of its potency. Along with being very potent, it is unique in that the pleasant effects don't really increase with the dose, but the unpleasant side effects do. For that reason most people that take it recreationally take a low dose of 1mg or less (2mg if they have a decent tolerance, and 4mg if they have a high tolerance).
It is not a good drug to take with no tolerance or a low one since so many people end up getting nauseous from it, but if you are set on taking it then I would recommend taking 0.25mg. Keep in mind that it takes a while to peak, so don't re-dose thinking it hasn't hit you yet if you aren't where you want to be after a half hour or so. I would wait a good hour before taking more if you feel you need more, and for me it takes almost 3 hours to peak.