1. Wear ballistic eye and ear protection
2. Stay away from exterior rooms(with exterior windows/doors); defend from interior-most spaces
3. Right angle barriers & turns (walls, corners, door frames) are your friend with regard to blast waves
4. Use window treatments (curtains, glass film, Venetian blinds, etc.) to prevent assault force identification of...
5. Barriers fastened/nailed to interior of windows and door frames (plywood, heavy blankets, thin mattresses, carpets, etc.)
6. For obvious entry points or rooms you can't defend, string the space with tanglefoot strands of heavy gauge steel wire or barbed wire...spread across the room at random angles at about shin and waist high. Anchor the wire into masonry, studs, or heavy furniture with eyebolts, heavy brads, nails or screws. This will slow up the entry team as they breach.
7. Spread fine (small grid) fishing net tautly across windows, hallway turns, staircase landings, etc. in order to cause a grenade to bounce back on the assaulters.
8. A piece of Home Depot's thickest Lexan or polycarbonate window section can be turned into a body bunker (with the addition of scuba webbing wrist/forearm straps screwed into it) that will deflect a blast wave around you. Just like a Roman legionnaire's shield.
9. Interior body length low wall of sandbags; you diving prone on one side, the bang detonating on the other.
10. Use a softball bat and wait for the pitch...
You do realize that, at the point a flash bang rolls or gets pitched into the room, you have only a few more seconds to live (if you resist)?