All the above suggestions are valid, of course. I'll offer another one: invest in a pocket calculator that works in feet, inches, and fractions. It's one of the most useful tools you can have on your workbench.
I've got one in front of me - one of the first such calculators that were introduced, I think - that I bought at Radio Shack more than twenty years ago. It's called a "Decimal-Fractional-Yard-Foot-Inch Calculator," and I paid about $35.00 for it. It still works perfectly. Nowadays you can pick up a calculator that will do the same things - and convert between the imperial and metric systems - at Lowe's, Sears, or Home Depot for considerably less money. (The more expensive ones also work out contractors' prices, work roof pitch problems, and do all sorts of other things that aren't relevant to model building. The cheapest one probably will be more than adequate for a modeler's purposes.) I picked up one at Wal-Mart a few months ago for $7.00. I keep it in the workshop and the old Radio Shack one (which feels like a member of the family) at the drafting table.
Highly recommended.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.