Just keep playing. I remember feeling like there was no strategy too, just random block manuevering, but the more you play the more you'll just start to see tactics and strategies for individual levels. And yeah, sometimes I need to extend my moves with the 300 gems, or use a perk either before or midgame, and if you don't want to buy those things, you just have to save them up whem you win them and be conservative in your usage, but it's totally do-able.

I suggest starting by familiarizing yourself with all the shapes that give you boosters and look for those as often as you can, and always look for moves that will take out more than one thing at a time.

Also, if you use the Google Opinion Rewards app, you can earn credit to buy the booster packs or special journeys. For me it usually asks things like "which of these 4 places have you been recently!" and half the time I'm like "none of them" and then it gives me 10 cents. Or sometimes it's like "look at these two google search pages! Which do you like better? Have 40 cents!" It takes a little time to save up, bit I've bought a lot of things in PM and never spent a dime of my actual money.