I have a level 97 main and several other pure and skiller accounts and I've played on and off for just about 4 years now, so I know what I'm talking about when I give advice to other players!
First off, there are 3 main types of accounts; the main, the pure, and the skiller.
The main- it is the account type which usually has the highest combat level. They are
Generally accounts that work on pretty much every skill. (The secret to combat success as a main is to balance your attack, strength, and defense levels!!!)This means you need to have a wide interest in the Runescape skills, simply because you'll be working on all of them to maintain a high total level. My suggestions for new players planning on making their account a main are to get combat up first, kill goblins (the key to getting fast combat levels here is to make sure you only have 3 items out while doing so! This will save you money because you wont need food, you can just die, put your 3 items back on, and run back in a matter of seconds) once you are about combat level 12, kill cows. Pick up the cowhides, go through the gate to the desert and drop them off in the bank and sell later for profit! Once you reach about 200 cow hides, sell them and buy the best armor (and weapon!) you possibly can. Beyond that, you can do pretty much what ever you want to do, woodcut, mine, smith, fish, cook, or work on combat, the choice is yours, and that is the beauty of Runescape!
The pure- a pure is a special type of account that is based off of 1 or 2 combat skills. The
Most common and suggested skills are magic, range, and strength. The key concept in pure is to keep the combat level low, but still be able to hit surprisingly hard. I would suggest magic, but this means you also need to have a money making skill that doesn't get combat levels! Magic is the best in my opinion because you can attack at range, hit hard, and even freeze you opponents so you don't have to worry about hp as much. The only problem with magic is; it's expensive! Another key point if you are going to get magic up, the safest way without getting any other type of levels is to use any teleportation spell as soon as you get the level to do so. This way, you get faster experience, and nothing is there to attack you/ you don't have to wait for a monster to respawn.
The skiller- the skiller is probably the most challenging of the three types of accounts. A Skiller is an account in which you get every non-combat skill up as high as you can, but remain at level 3. This type of account proves to have many challenges when moving from place to place because of the low hp level. Also, when you are working on a skill like woodcutting for example, you need to run away the moment a tree spirit comes to attack you. There really isn't much advice for this type of account except what I have learned from my experience. Vary what you do! If you say, hey, I think ill smith 2k steel bars today, THINK AGAIN! This game is for fun and don't forget it, if you just do boring things all the time, what is the whole point of it? So make sure you do things you enjoy doing as a skiller, even if you do need 2k steel bars, cut up the work into sections, like smith 500, do something fun and repeat!