Take my advice as I'm a veteran ftp player killer, 3,000+ bounty rank.
If you're making an account that has more then 40 defense, range is the best option. Not only is it fast, and consistent, but its also penetrates players with high defense. A level 102 (99 range, 99 life, 99 def), can easily out hit even 120+ combat players, if they were to use melee. Another advantage is that you can shoot from a distance, and with magic being ever so limited, it's hard for you to die, unless your opponent also has range. Note, although a rune weapons, such as a scimitar, is least effective as compared to a bow, rune weapons will hit higher. This still shouldn't be a problem, if you were to death match, since, as stated above, range is consistent. Nonetheless, it would be hard to deal a finishing blow, unless your opponent forgets to eat, but it'll be least likely, since most ftp player killers safe a lot. In addition, when ranging, one might consider dungeoneering for a long bow sighted. This is because you can add more defense bonus to your gear, since you can wear full rune, instead of dragon hide. Don't worry, since the bow is very accurate, and you'd still have 100 + Ranged bonus. Furthermore, if you're every so bored, try to get some strength levels up. It's also ideal to limit your attack to 40, since if you were to get extra levels, it wouldn't help in ftp and give you a disadvantage with the extra combat levels. Range to 2h, the delay, is the best for player killing if your below 100 combat. Even If you were to become a pure, and use range, at 70 + even if you have all other stats as 1, you'd still be able to hit through rune.
On my last note, remember that there are other players that can have similar stats to yours, and runescape involves a lot of luck. You might not always win, but be persistent. I also disagree with some posts above, that you need members to make money. Once you feel comfortable player killing, you can alternatively high risk with players, i.e, bring some money and fight. Just don't get scammed though, since if someone trades you and shows X amount of cash in trade, once they decline, the money will be in their pouch. In order to avoid this, they have to offer a certain amount of money, and then remove it in trade.
Best of Luck, young tadpole.