I am still fairly new to the scene, and on my first pin. While advice will not be short around here, my suggestions would be to:
1 | set a budget range first and what category of pin you might like - prices for serviceable good working DMD pins with decent themes start in the low $2K range when you can find them to new pins $10K+
2 | go through the top 100 on Pinside, pick several themes you think you may like, and watch the videos
3 | find places with pins in your area and actually go play - and by all means if you are anywhere close to a pinball festival then go
4 | find the pin specific threads you are narrowing your interests down to and read through them as this will give great insight into the games
5 | search this site, monitor CL, etc. for deals on pins if looking for a used machine
6 | find someone in your area that really knows about pinball that can help you make an intelligent buying decision - look for facebook clubs, people from your area on Pinside, etc.
7 | buy something that you want and like, who cares what someone else may think on this site - there are lovers and haters of every pin ever made
8 | put extra money aside unless you are buying a brand new machine as you will have things to fix, mod, etc.
9 | hone your technical skills as you will want to be able to make adjustments and fix most things yourself
10 | get to know the reputable pinball parts suppliers as there are many great ones, but also a few charlatans out there
Most of all, have fun! This is a great hobby with great people who all share a common interest and are happy support, have fun with, and hang out virtually with you.