Kiedon

The easiest way to collect swamp tar would probably be picking it up off of the ground in the lumbridge swamps, this requires no skills. If you have 17 slayer you could also try killing cave slimes, cave slimes always drop in between 1 and 9 swamp tars each kill.

I would try to set a daily goal so that you don't get bored trying to do the same thing all day. Try doing something like mining some amount of ores or some amount of exp everyday you have a decent amount of time to do that, and then after you do that goal you stop working on that skill until the next day. It might help taking breaks and playing some minigames and other things.

I would raise prayer because prayers are useful in many situations, and more prayer lets you use them longer.