Make lists! List all your "must-haves". And then list all your "really wants". Make sure you know what you want - you want to get the right machine and also make yourself a bit resistant to any salesperson who might try to talk you into a machine you don't actually want or need.
Test drive several machines, from several different manufacturers. Buying a new machine is a lot like buying a new car but it's ALSO a lot like buying some new shoes - what's comfortable for me might be terribly uncomfortable for you!
For example, I like Janome - their machines are high quality and when I use them they feel extremely intuitive and "natural" to me - they do what I expect they will do and I've yet to sit down in front of a Janome and feel intimidated or confused by it. Bernina is another brand that has an excellent reputation, but their machines feel "foreign" to me and do things I don't expect, so I don't like using them - I feel confused and clumsy. So, I bought a Janome and I've been extremely happy with it. I could probably get used to a Bernina and end up happy with it too, but to me it seems more sensible to buy the machine that I immediately felt comfortable with.