If when playing your character you find yourself unable to use skills because of a lack of energy your build is probably in need of work. Casters normally need a skill or two devoted to regaining energy about runescape gold. Warriors absolutely require a speed boost skill or they will spend all their time chasing sniggering monks in circles, as well as an attack speed boost to help gain adrenaline. Do not try to defend against everything in your build - being a threat is much better than being unkillable about runescape gold. Warriors especially should not be carrying significant defense since they will typically be one of the last targets chosen about runescape gold.
When choosing armour, read what it does carefully. For example, Knights armour reduces damage for warriors but the effect does not stack - so you are better off picking just one Knights piece (typically boots) and having a better armour level on the larger pieces (chest and legs). When choosing weapons about runescape gold, there are some easy choices and some others that are more dependent on personal choice. At the time of writing, the Staff Wrapping of Enchanting is a must-have for any character with key enchantments about runescape gold.
Do not use more than 1 Superior skill rune - the health penalty is too painful. There is no reason not to use minor runes of your other primary profession skills and a superior rune of vigour. Warriors will also usually want an absorption rune. Do not pick skills or use tactics based on the assumption that your opponents will be bad. They may well be but then you will win anyway. Worry about the cases where you will face someone who knows what they are doing.
The single biggest difference between PvE and PvP is probably that positioning matters. You can get through the whole PvE game and never move when monsters are beating on you. This is not the case in PvP.