To make my 4e Game more gritty. I plan on doing the following.
1. Depending on what the Health-roll system is like, go with the weakest version of it, so watered down HP to start.
2. The gear including weapons and armour of the PCs will be of poor-make, so wouldn't give much bonuses in combat. As well as being more likely to break, be punctured, etc.
3. Have them face foes at the very top of their ability to fight. Also multiple foes, so swarms of orcs, etc. I want to see them reeling at the end of combat. Their characters/players on the edge, their powers drained, their armour mudded and weapons dulled. They then have to seek out shelter to recover and during recovery risk the creatures/people around them possibly be of ill-intention (this would be dependent on rolls and myself the DM; I don't want my PCs to die).
4. To sorta go along with 2. it is a low-magic game, with few items to help you, and magic itself is erraticate and time-consuming for non-offensive abilities (no insta-heals).
5. Definately hoping for a good social-system, since that will be key to my game.
6. Possibly introduce flaws, and fear-roll/systems into the game, to give a representation of how fragile the PCs are (it won't be that forced, but hopefully the players will RP-well and take the rolls to match it thus).
7. Finally and I think most important is simply to create a mood/atmosphere and a world that is gritty and harsh. No matter how you tweak the rules, if the game is set in a happy, bright and peaceful setting that mood won't come across.