Installing adjustable shelf standards is an inexpensive solution for storage and organizational problems.
Select the area you would like to be shelved. Divide the width into sections that will place the adjustable shelf standards about 18” apart keeping the first and last standard about 6” in from each end.
Then decide the height of the lowest shelf and purchase standards that will be about 16” from the ceiling. The standards can be purchased in 12” increments, 24, 36, 48, 60, 72-inch are easily available. Standards are available in assorted colors also.
Mark the top of the first standard and lay out the spacing for the rest at the top screw hole.
Now use a level and mark all the top holes.
When working on a drywall wall I use an E-Z screw in anchor for a #8 screw when the studs do not fall where I want the standards to be. Install the top anchor and hang the standard loosely. It will now act as a plumb-bob so the rest of the holes can be marked nice and level. See MrsHardware.com Wall Stud Finding Tool
Install the rest of the anchors and screws and you are ready to hang the shelves.
For a heavy desk top use reinforced shelf brackets and screw directly into the studs for maximum strength.