Specifically with herblore you can increase your profits by making unf potions as well (combine the herbs with a vial of water).
Try getting 50 runecrafting through Runespan (which should only be a couple hours) and then take advantage of the Rune Goldberg daily to turn a profit. It can take a bit to get the hang of it but once you can afford (or make) some runes of most types you can generally come out positive every day.
You might also want to do some quests to increase your skill levels. They generally help to unlock useful things especially for lower level players. There are also a number of shops from which you can buy and resell stuff to other players via the Grand Exchange and make a profit - like runes, broad arrowheads, and so forth.
Hopefully those are some good ideas to get you started.
P.S. For Slayer generally you're gaining combat XP and sell the drops of monsters. It is not as beneficial until you get to the higher levels but it can be fun, make some change, and help to train a skill along with your combat levels.