A tournament's a marathon, not a sprint. It's always great to obtain an early chip lead, but it never means much unless you can keep it going.

Once you have the chip lead, your image at the table is going to be very important, especially in live tournaments. If players see you as a wild, loose, loud type of guy who just wants to have fun, I would recommend tightening your opening range, but at the same time keep talking a lot. Other players won't notice you changed your play style, and if you get a monster, you could stack them more easily. This is a good strategy especially if you won your big stack with a bad beat, since other players will already view you as a loose player.

The second one is more realistic, in my opinion. It consists in playing solid, but putting a lot of pressure on other medium/big stacks. Since they just won a big pot, and don't want to lose the little bit of chips they made in the beginning, you can put pressure on them very easily. If you use this strategy, well timed 3bets, and even cold 4bets can work like a charm (taken straight from the Vanessa Selbst playbook). 

As crazy as it seems, small stacks are what you need to worry about when you have a big stack. Small stacks need to gain chips quickly, since they are under pressure from the structure of the tournament. As the blinds go up, they are more likely to call off with a lot of medium strength hands, and will be flipping with you a lot of the time, putting small dents in your chip stack. I would suggest you to only get involved with them when you are trying to get value, since they are going to call with weaker hands.

Last but not least, implied odds. With a big stack, it's worth calling a raise from time to time with suited connectors or small pairs against players that you think are likely to stack off with top pair. Just  be careful, as this can turn into a -EV situation quite quickly if the blinds go higher and you're still using the same strategy. Also, if you are going to call with those types of hands, don't be a hero: your goal is to make a big hand and stack your opponent, and nothing else. No need to call down with middle pair, or an under pair; it's going to cost you in the long run.

I hope this helped you a little. I'm not a tournament player, but I think this will lead you towards the right path. Keep stackin' those chips!

nH.

couldnt of said it better myself. nice post

and remember to play your stack in position and with good hands like pairs, suited connectors, 1-gap connectors, I personaly would play some kind of small ball ( folding a lot of flops when getting some hostility) and putting pressure as NoHubris said on medium stacks.