An Easy Answer
To How Much Insulation Do I Need.
I still need to preface this with an obligatory warning: IT DEPENDS.
However, if you are reasonably well off, take vacations, don't forgo medical care to save money, and can risk a 10 yr payback if what I'm going to recommend is a bit more than you need, then, you probably can't go wrong simply doing the following, in order:
1. Attic:
Batt or blown in insulation: 24 inches, R72 max in one of following layerings:
Open floor joists: Install foil or paper faced, with face down, Full Depth of Joists, ie, if 6 inch joists install 6 inch batt, install air barrier (Tyvek) taping all seams and caulking or friction fitting down to tops of walls under eaves, crosswise to joists 10 in unfaced batt, offset 1/2 batt width another layer of 10 inch. Total 26 inches, R 78
2. Attic floor: Open up floor near eaves to determine where top of perimeter wall is, if the flooring is installed air tight to top of wall, skip to installing the air barrier. It there is a gap, fill with sealant up to 1/2 inch, spray foam up to an inch, after that you'll need to install a 12 inch band of tightly packed ROCK WOOL (not fiberglass) (Click here for more) around the perimeter of the entire attic, then reinstall attic floor tight to ROCK WOOL. Install air barrier (Tyvek) taping all seams and caulking or friction fitting down to tops of walls under eaves. Install 12 inch batt insulation lengthwise with second layer atop offset 1/2 batt width.
3. Prior Insulation: Remove trash, animal dropings, extremely stained insulation - to some extent you'll be breathing whatever is left. Fill in low spots with layers of 3 1/2 inch unfaced fiberglass batt insulation, fill in "cracks" between batts or push together. Install air barrier (Tyvek) taping all seams and caulking or friction fitting down to tops of walls under eaves. Install minimum 6 inch batts lengthwise down attic. If you aren't up to 24 inches total, add another 6, 8, 10, or 12 inch batt lengthwise offset 1/2 batt.
Note on friction fitting air barrier to top of perimeter walls below attic: This isn't easy. You need to be able to reach in with hands to place sealant and barrier, sealing to not just wall below but rafters and joists to either side. I couldn't do this as I had no attic floor, and 100 yrs of nails sticking down from the roof. Instead I PACKED the gap between attic floor joists / top floor ceiling rafters that sat atop the perimeter wall tight with ROCK WOOL, rammed a section of foarm into that, between each pair of rafters, sealed to rafters, flush with their bottoms, then sealed the air barrier to that. (Click here for more)
Note on attic access: If you need to access part of the attic even if just once every few years, install 6 inches of foam 18 inches wide as a walkway, sealing each to that below along edges, and to air barrier, and packing batt insulation tight to sides.
Note on lights and fans: Fans must be connected to ducts leading to outside. Lights, unless you are an expert and know it's not necessary, must be boxed in with gypsum board at least 12 inches away from edge of lights, sides and top. Obviously you'll need to "hump up" insulation over these box outs to maintain depth.
Doors, Windows, Base and Crown Moldings: Make as airtight as possible without replacing. Sealant around all trims, between trims, between trims and walls and / or paint. Replace loose window putty. Make sure all windows and doors close properly. Install metal and felt, metal and rubber, or plastic and vinyl weatherstrips as needed to close gaps drafts can be felt through on a moderately windy fall day. You can't stop all drafts in high winds or frigid days. Even new metal or vinyl windows won't do that.
Note: Unless the windows are in dangerously bad condition or extremely ill fitting it is never economical to replace. Inch for inch LCD screens are the same price as high performance windows, and more fun to watch usually. Inexpensive retrofits often leave considerable gaps around windows negating the improved air sealing.
Foundation above ground: Insulate - See Frost Proof Shallow Foundation on this site, (Click here for more) or if all else fails, 4 inches foam secured with nails or screws to foundation walls or to plastic lumber secured to foundation walls, cover with Dense Glass or Cemeent board or stucco (including thin coat synthetic "stucco"). Run at least 12 inches below grade. Backfill with gravel 6 inches under and infront of foam and cover gravel with 12 inch square pavers sloped away from house.
Foundation below ground: Occupied: Insulate inside.
Foundation below ground: Unoccupied: See Frost Proof Shallow Foundation on this site. (Click here for more)
Exterior Walls: Siding to remain:
No insulation: Hire contractor to blow in HIGH DENSITY CELLULOSE only, nothiing else. Have contractor provide pics from a thermal imaging survey when done to show no gaps.
Existing insulation: Hire investigator / contractor to do thermal imaging of house on cool day with heat on. If limited areas are problematic they could be addressed by injecting foam. If susbstantial problems, the contractor may be able to blow in more insulation or add a layer of foam insulation between old batt and outer wall - this isn't gaurentable / predicatble work, so you'll need to research you contractor enough to trust them, and of course, have them do a thermal imaging test afterwards.,
Exterior Walls: Siding to be replaced:
1. Remove siding and window trim.
2. Blow high density cellulose into stud cavities.
3. Install air barrier (Tyvek) with all seams taped and taped top and bottom to rim joists. At windows tape and seal to wood sheathing around window.
4. If not superinsulating (and why aren't you - see super insulation at this site,(Click here for more) ) install two layers 2 inch high density ROCK WOOL boards securing to building by furring fastened with special stand off screws that will keep furring all at the same distance from sheathing.
4. If superinsulating furr out walls 8 to 10 inches (see Super Insualtion Retrofit Wall this site ,(Click here for more)). Fill cavities with ROCK WOOL, Blown High Density Cellulose, or Batt fiberglass instulation.
5. Install air barrier (Tyvek)
6. Install siding on furring.
Why did I say DON"T DO THIS, or USE THIS, or list manufacturers? Can't other ways work. Of course. However it's hard to imagine how these installations could fail, while it is very easy to imagine how other ways could fail. IT DEPENDS , (Click here for more) . If you want a tailored solution, hire a licensed architect or enginner or use a contractor your most trusted friends and family can swear by, and who has been doing insulation work at least 20 yrs. 
