First measure your framed opening to ensure that it is no more than ½” larger than the window all the way around. Next check the opening to be sure it is square, level, and plumb.
To check square: Measure window frame diagonally. Measure from the top left corner of the frame to the bottom right corner and from the top right to bottom left. If the measurements are equal, the window is square.
To check level: Place a level along the sill plate. If the bubble indicator is centered, the unit is level.
To check plumb: Place a level vertically on both the interior and face of the left and right jambs. If the bubble indicator is centered, the unit is plumb.

Next you will need to Flash the opening. Apply 8” to 12” of Bit-o-theene to the opening. Position the Bit-o-theene so that approximately 1 “ will overlap the sill. Run 12” Past each side of the opening (right).

Run a continuous bead of silicone caulk around the inside perimeter of the nailing fin where the nail fin engages the window receptor (see right).
DO NOT CAULK THE WEEP HOLES. If the rough opening is larger than the window by 1/2" or more, apply silicone caulk to the sheathing, making sure the bead is no more than 1/4" from the edge of the opening.

Now place shims at each corner of the rough opening where the jamb meets the sill plate. With the sash closed and locked, insert the window from the outside and rest it on the shims.  Be sure there is a gap between the sill plate and window frame to allow for fluctuations of the wood. 

Place a roofing nail in the top corner of the nailing flange. You will need to check the window to be sure it is square, level, plumb, and centered.

Measure the unit diagonally in both directions to ensure the window is square (see right). If the window is out of square or the sill is bowed, the meeting rail may not seal properly even if the sash lock.
Check the sash where they meet the jambs to be certain the reveals are even. If there are any uneven reveals (gaps), adjust the shims to bring the jambs squarely against the sash. The weatherstripping should touch the jambs but should not be compressed too tightly against them. Look for an even gap between the sash and the jamb from the top to the bottom.

Finish putting the nails into the fin of the exterior of the window. Do not nail in every hole. Recommend every third hole on sides and bottom; the top will only need two on across the top. The nails must penetrate the stud at least 1”. Adjust size as needed.

Now pack insulation around the window frame, on the interior, between the frame and the opening. 
Apply bit-o-theene to the jambs of the window, starting 6” above the head of the window. Run a continuous strip along the jamb. The strip must cover the nailing flange, extend 6” below the sill, and overlap the paper at the base.

 After you have applied the jamb paper, run a strip of paper across the head. Be sure to cover the nailing fin and overlap the felt on the jambs at least 6” on each side.

Finish off the exterior of the window. If applying brick, stone, stucco, etc., make sure to leave a 1/4" gap around the entire window frame to allow for expansion of materials and mortar. Use trim coil stock to cap off gaps and trim the opening.
Be sure to use the proper grade of silicone caulk to seal the entire perimeter of the window (see right).
Do not leave any gaps where water or outside elements can penetrate into the home. Use common sense to complete the exterior. If an area appears to be prone to air or water infiltration, seal it with coil and/or caulk. Make certain that the weeps on the outside of the window are open and that water can drain from the sill and out of the weeps.

Finish off the interior of the window. Check the window to be sure it operates properly (see right).