This is a lot easier when you realize you can have a vassal form Prussia. Then you're not expecting AI to do something great for you.
My general strategy was to form Nepal ASAP. Once you do that, use some alliances to conquer northern India and the Himalayan mountains. You want to build a decent size nation before you even consider Prussia.
Once you have a base, you have two choices:
Snake towards Europe, which is probably going to include fighting Muscovy, Commonwealth, and/or Ottomans.
Wait until the age of Revolutions bonus 'Ignore Coring Range.'
I started snaking but decided to wait and spend my time building up my economy. Watch for Brandonburg. If they are Protestant or Reformed, and less than 100% war score for their provinces (admin efficiency and war score cost reduction will help), no CB them (or wait for Imperialism) and vassalize them. Once you do this, feed them the cores they need for Prussia: Königsberg (41) and either (Danzig (43) or Stolp (2995)). I made them pretty large (around 300 dev), and they formed Prussia by themselves.
Once they form Prussia, you're going to want them to get a decent standing army, at least 50k. Hopefully they have some manpower too. I subsidized them and waited. Once they have the army, break vassalization and immediately dclare on them (truce break). You can get them 1 on 1 and kill all their units. Just keep killing them until you have over 100k, and then peace them out (you have to win the war, so take something from them).
Idea group recommendations
Since you're in India, institutions are going to hold you back. You should get either Economics (so you can dev institutions cheaper) or innovative which give you straight 10% tech cost reduction, +25% institution spread, and -10% institution embracement cost. The other benefit to innovative over economics is that the military policies are amazing (more on those later).
You'll want Innovative/Economics, then Offensive. Offensive gives you siege speed, discipline, force limit, shock and fire for leaders, and the Innovative/Offensive policy card is +10% siege speed and a siege pip.
If you're using Vassals, go Influence or Diplomatic. Otherwise, go Quality. Quality gives you 10% CA for Inf/Cav/Siege, +5% more discipline, and if you went innovative you get another 10% ICA with Innovative/Quality
.
You'll want Religious or Humanist, and Admin. I waited far too long for Religious (group 7), and never used Deus Vult. You could go Religious in idea slot 3 to get Deus vult, since you don't get a lot of claims.
Things to watch for
A lot of India is Sunni, so be careful of causing AE towards Mamluks/Timurids/Ottomans.
In my game, Timurids stayed strong. It was very difficult to try snaking.
If you can't snake, you could try getting a vassal in Europe with a no CB early, or just wait until you feel unstoppable. I didn't get Brandenburg as a vassal until 1709, and finished the achievement in 1761. You have time.
If Catholicism stayed strong, you might need some help to secure the required provinces for Prussia. Watch for allies in the area (Mamluks/Ottomans) who are going to hate Catholics.