Prayer is one of those skills that is pretty straightforward. Bury bones to get experience. Different bones give more experience than others and you can do things like ectofunctus or your player owned house to get a bit more experience. But the idea is the same. Get bones, use them for experience.
If you have a huge cash pile you could go out and buy all of the bones you’ll need. It’s almost 3 million bones to get from lvl 1 to lvl 99 prayer. At 61 gold each that’s quite a bit of cash to blow on prayer. You can buy bigger, more expensive bones to make it go faster, but that still means loads of gold. I prefer the cheap way, letting others do the dirty work for me.
First, chickens. The chicken pen in lumbridge is always full of people. Dead chickens, and their bones, lay scattered all over. No one picks up the bones because the bank is far away so they just sit there, ripe for the picking. Head on over, pick up the bones, bury them. It’s a near endless supply as chickens die respawn quickly and die just as fast. You’ll find it hard to pick up everything you see, but that’s a good thing. On top of bones people often leave feathers on the ground. I pick them up because they only take up one inventory slot and being in the 15-20 gold range the value adds up quick. Remember, chickens can drop 5-15 at a time. It wouldn’t be hard to get a few hundred feathers in just a few minutes.
Another favorite of mine is the minotaurs in the security dungeon. There are always people, bots really, here killing the beasts. Like the chickens, it will be really hard to pick up the bones fast enough. Minotaurs also drop arrows which people generally leave alone. The price for these adds up just like it does with the feathers. Or you could save the arrows and train some range later as well.
The main thing is, pick somewhere that’s crowded. Sure you could kill creatures, pick up bones, then bury. But if others are there to do the real work (killing) you can just pick up and bury. It goes much faster and gets that prayer up quickly. Pick up items that are stackable. They take one slot, you can get as many as you want and after a while the price of those cheap items add up.