You will need to have a selection of tips handy for clients nails that are flat or very curved -- not just ones that are "standard" in curvature.  Also, consider that some women's nails are very wide while other women's nails are very narrow.  Therefore, you may need a brand of tips that includes an "extra wide size 0" tip.  In the salon, you should have one box of tips for each of these FOUR kinds of nails so that you need not turn a client away because you do not have the correct tips to apply. And consider this:  The tip is only as good as the glue you apply it with... so purchase a quality adhesive.