For that last few months I have slowly been doing shattered heart each week for the quick XP boost. Once I get my weekly quota of rocks I then work on combat and slayer. A couple of weeks ago I hit the 98 Constitution and at this point I am now about 50+k away from the 99.
Too many people find it boring and use 'bots' (that is for losers and may be the subject of a future blog), but, I find that if I spread out my work among many tasks I don't get as bored. One of the other alternate activities was penguin-hide-and-seek. Once a week I get my 16 points and can apply it to whatever skill I want. It takes about 30 minutes using one of the clan chats that is for the event. The newest one I have tried out is troll invasion. You can only do this once a month, but, if you make it to the end you get a massive XP reward (last one I did I got over 50k for summoning).
I am planning a small '99' party with a few friends and acquaintances that play RS and pass out a few items to celebrate my milestone.