Welcome. This guide was 100% made by me off the top of my head through some experience. This does not include rookguard, too.
At level 8, you should have at least 500gp from rook or so to buy some eq. I suggest maybe a scale armor for about 80gp, a dwarven shield for about 100-150gp, brass legs for about 100gp, and a decent wep for your class which is cheap.
After that, I suggest training. Now you could either do this at Trolls, but I prefer Rotworms (though they can hurt). I usually hunt them for a bit, make some more cash then buy some better eq to block them better. A plate set, dark/steel helm and your dwarven shield + wep (and a scarf from Edron [15g]).
So after training to about 35/35, hunt some more (until maybe level 11). At level 11, train till 45/45. Now you'll be able to pwn a bit more. Hunt some more rotworms until about level 16 and use the cash to buy better eq once again (or have a p-set and a good wep such as a knight axe, fire sword or a decent club by now).
At level 16 with 45/45, I suggest larva. Hopefully by now, you should have decent enough eq. Go to Ankrahmun and find some larva spawns. Hunt there until about level 20. Now this is when you have to train again. This time to abut 50/50 or 55/55 (which ever you'd like). After this, you should have better eq, so go back and hunt some more until level 25. At level 25, go back and train again till about 60/60.
With 60/60 and some decent eq (maybe a c-set if you're lucky) .. you might want to try scarabs. Have some UH's and some mana fluids (if you want to buy them) and hunt scarabs until 30. This will get you quite a bit of profit if you know how to hunt them with out a huge UH waste.
At level 30, go back and train untill 65/65 or 70/70. I'd prefer 70/70 as it's easier to hunt then.
Here again, you have 2 options. You can either go to cyclopolis in Edron, or still hunt scarabs (though it might be boring but it's up to you). Scarabs I'd say would be faster as there's always a ton of people in cyclopolis, but you can decide. After reaching 40, you should have enough profit to buy better eq and more UH's.
At level 40, I suggest you train again. This time until 75/75 or 80/80 (not much more training after this). You can hunt where ever you like. Which ever suits you. I'd suggest scarabs, cyclopolis, dragons (if you can make a profit or have enough UH's to use), or tombs (again quite costly with UH's depending on what you hunt).
Any level past 50
At any level past 50 (I suggest before 70) .. train till at least 85/85 or 90/90. You should have some good eq like: Royal Helm, DSM, Crown Legs, BoH (Steel boots if you want instead or both), Demon shield or MMS, and an AoL or Plat ammy (depending on how much that's all worth). With this eq, you'll be able to explore better and hunt better. With 85/85+ you'll be able to hunt Dwarf Guards with making a good profit. This is a great way to make money. If you know how to get here, I suggest the 'grid'. If not, go to any other Dwarf Guards. Gather everything you can sell to an NPC, food etc etc. Scale armors can get you a great profit, too. 75gp each so collect those for sure.
Take in empty bp's of your own as you'll be needing them. After you're comfortable with exploring other places, then go for it :).
And this is my guide on how to level up a Premium Knight. I hope it may come in handy, too. Oh and skills and eq play one of the most major roles in making profits.
Old Tibia features
Ultimate druid guide
Fast leveling guide for sorcerers
Level 8-70 in 2 Months
Rook tutorial: Premium and Free
Addon items list
Quest outfit addons
Tibia premium account addons
Tibia Premium Account outfits