Well it depends: Are you starting out with money? If so, how much? Members?
If you're starting from scratch, I would start with your basic money making skills: Woodcutting, Fishing, Mining, Runecrafting, Thieving, etc.
Get these to 70 each, then start working on other skills that either cost money or don't make money (Firemaking, Farming{can make money w/herbs}, Smithing, Herblore, Construction, etc.) Get as many of these to 70 as you can with the money you've made from your money-making skills. Continue this process until 99 for each skill.
YOU CAN ALSO MERCHANT/FLIP WHILE SKILLING
If you're starting with money, you have a few choices:
1. Don't spend a dime on skills and just merch/flip
2. Spend it moderately on skills that cost money and work on money-making skills at the same time
3. Blow it all on expensive skills and work on money-making skills when you feel like it
Personally, I use method #2 while also merchanting/flipping. I take breaks from a certain skill and work on another for a little while, then come back to the first skill. For example, right now I'm working towards 99 construction (currently 91/99) and I take breaks every now and then to train slayer.
If you have any questions about skilling, or anything else feel free to PM me!