Using Normal Grenades & Mirvs:

1. Normal Grenades
You MUST learn to use normal grenades. They are vital.
2 Good situations to use normal grenades:
1) When you are reloading
2) When you need to throw extra far
I recommend using a grenade timer. It is not a cheat, and is available at many other TF sites.
When you are fighting on the bridge on 2Fort5 or a similar map, Normal Grenades are great, since they will go farther with more power.

2. Mirvs
A lot of people under estimate the power of a mirv.
3 Good situations to use mirvs:
1) You're almost dead, with several enemies around you. Just throw mirvs, you will almost always take at least one enemy out.
2) In front of respawn. It might be considered a 'cheap' tactic, but it works for suppressing respawned defense.
3) When you are on defense and go to resupply. Just drop a mirv or two, and go get supplies.

Gren jumping is also useful, but it is covered later.