Alignement

[Ewan Chrystal]

depends where its to go. if for instance you want the text 2 inch down from the top, wrap 2" masking tape round the top of the glass. That will give you a straight line 2" down

[Martin Pearson]

Like Ewan says it depends where on the glass it is to go, also would depend on what sort of glass & quantity.
If I were to be doing a lot of them then I would probably look at making a jig for the glass to speed up production, if there were a lot of curved glasses then I would look at producing the text on a curve so it was straight when applied.

The more detailed you make your questions then the better the replies you are likely to get.