FWIW These are the steps I used when I converted from "steam" to "glass" back in 2013.
1) Select the brand of equipment you will use. One of the most, if not the most, important factor should be company longevity. You don't want to get stuck with an orphan EFIS. Now, don't get caught up in what features are available today as that changes incredibly fast.
2) Replace your current AI with a small EFIS like the Dynon D6, Garmin G5 etc. For now keep the rest of your "steam" gauges. Fly this configuration until you are comfortable reading the different presentation of flight information on the small EFIS. An added bonus is that this makes for excellent "partial panel practice" as you migrate from reading "steam" to reading "glass".
3) Make your final decision(s). You can now install your existing small EFIS as the backup device since you are already comfortable using.
YMMV
