If you search around there's thousands of threads with answers to what you need.
You should start by waiting until you're in full acute withdrawal. This means your eyes and nose are running like faucets, you're sneezing 14 times in a row, your joints and bones ache and your legs are kicking like you're riding a bike.
Once you're there, you can take your first sub. I'd take an 8mg tablet or strip and cut it into 1/4's, and take each 2mg piece every hour or so until you feel normal. For me, my first dose here is usually 8mgs but sometimes more. Just take 2mgs every hour or so until you're held.
From this point on, I recommend a RAPID taper, reducing by about 1mg/day (I reduce 2mg/day myself, but that's just me) until you get to the sub-1mg dose ranges. I usually go a few days at 0.5mg and maybe a couple more at 0.25mg and then jump off feeling great and as if I've completely cheated nature. This usually takes a week or two to go from first dose to last dose and first fully opioid free day. Don't spend more than 2 weeks using it.
Don't take too much. There is a ceiling effect where any more will no longer produce noticeable effects. And don't get antsy and take them too soon before you're in withdrawal or you'll worsen your withdrawal before the bupe begins helping.
You should know two things - 1, buprenorphine is very powerful. When I had no tolerance, 4mg had me nodding for 14 hours and high for 24. 2, it has a long elimination half-life. Two days after your first dose, you'll still have some bupe bound to your receptors from that very same administration.
