Tom, you came to the right place. This is the best pro shop in town!

First off we will need alot of information. Everything about your bow and equipment and setup. We need to know what arrow rest you are using, arrow length and size, field point and broadhead weight, etc.

Give us all that information and we can get started on helping you.
Well, actually we will get started right now.

Tuning isn't all that hard. The hardest thing of all is your nocking point but the proshop guy probably got it right when he put it on.

With the side to side fish tailing, if you are using a two prong type of arrow rest, it is easy to correct.
First, eyeball it to see if the rest is obviously too far to the side. Nock and arrow and look at it. If it is obviously too far to the side, then you know you need to move your rest in the opposite direction untill it is aligned and the fishtailing goes away. Make small adjustments until you got it right.

Now, if there is any fishtailing, move your arrow rest up or down to correct it. I just re read your origional message and you said a salesman sold it to you. Well, hopefully he put the nock on right so you don't have to worry about it. Otherwise if you move the rest up and down and the porpoising (if there is any) doesn't go away no matter what, then you might have to try adjusting your nock up or down until it goes away.

After you got the field point flying like bullets, try broadheads.
I just tried my broaheads and they kept shooting left quite a bit.
Broadheads are very sensative to minor tunning problems. Slight adjustments with your rest that don't affect field point accuracy can affect broadheads.
Luckily I had a NAP Quicktune 3000 micro adjust arrow rest so adjustments are easy.

Make sure it's not fletching clearence. That could be part of the problem.

Get back to us with your setup and we can help.

Nic