Wear a bow. If you're a skiller, it's important to wear a bow with no arrows at all times to avoid those accidental combat levels. Turning Auto Retaliate does not solve this problem, as you can still simply attack something with nothing but a click. A Shortbow can be purchased at the Grand Exchange and the Training bow can be purchased from Beefy Bill who can be found north of Lumbridge.
Don't 'overdress'. Skilling normally requires a lot of running, whether banking or possibly running to a certain location. It is advised that you don't wear heavy equipment; such as armour, and when skilling, armour is usually not required. Although if you wish to wear armour, it's best if you wear weight reducing items such as Boots of Lightness or a Spotted/Spottier cape (requires 40 - 66 Hunter).
Invest in skills, not items. Many Skillers spend all their money on expensive items which are not needed. It is common that Skillers get bored, and decide to buy expensive items/outfits they don't and will never need. It'd be so much better if you took that money and invested it in skills, as a simple Skillcape can show all of your wealth and experience.
When you do buy things, think long and hard about it. Items that could save you from dying, causing you to lose millions are something that every Skiller needs. The best items known for this would be the items with good defensive bonuses (possibly an Amulet of Fury), something that could teleport you away from danger (a Ring of Life), and/or something that could heal life points, twice as fast (a Regen Bracelet).
"What 1f 1 want to express m3 99z"? If you feel you want to express your 99s, but can't, due to the Spotted/Spottier capes, you are capable of wearing a Hood, however this will be an extra 0.4kg, which isn't too bad when compared to other items. If you want to fill those empty left places, such as the torso and legs, go ahead, but it is recommended not to.