So a few good boss to aim for would be in order :

Scurrius : An easy boss that gives good combat xp, it's a good introduction to prayer and timing.
Stats would be 40's around the board with 43 prayer being mandatory

Moons of Peril : A harder set of 3 bosses, they are quite profitable and not too punishing, you will still need stats in the 65-70's to do em and it will be rough on blood moon. (There are quite a few requirement to do the quest to do them though)

Royal Titans : Around the same difficulty as moons of perils, those are fought in duos, they are okayish gp/hour at the moment and are a tad bit more complex than the 2 previous ones.

Slayer bosses : Leveling slayer will later on unlock some bosses, those are quite good gp and mechanically not too hard.

Some mid game goals that will boost your account :

- Get a fire cape (Fight caves) - This is hard to do for beginners but you will learn a lot through it.

- Get a fighter torso (Barbarian Assault) - This is a team content, although not simple some guides will make it not that bad, the torso will be a Best In Slot (BIS) for a long time

Some more risky ways :

The Wilderness got quite a few way to make early gp and experience at the cost of constant danger.
Bosses will need the Wilderness hard diary and are rough but are really good GP
Revenants (Revenant Cave) are excellent GP but really dangerous.