Staples and glue are my friends. Lots of glue with the staples just holding the wood together until the glue dries.
Nails only for finish or if there is a sheer load. Ever break off a "dry-wall" or "multi-purpose" screw when it gets bent? Those screws are very brittle - lots of compression strength, no sheer strength. When building ladder or step units that have sheer loads on them I will screw them together to get a compression force between the two, then I'll add a
nail. Wood screws are generally stronger, but take more time to use properly.
I actually took a 2 x 4 and drove a
nail, screw,2
lag screws (one pre-drilled ,one not) and a
bolt through it. I then split it in half to
reveal the holes each one made in it. The screw was the least destructive to the wood. It had the smallest hole and seemed to repair itself better. Bolts are very strong as long as you use the same hole every time and don't re-drill in the ends of your
platform or legs.
Lag screws require pre-drilling to work properly. Try the experiment I mentioned and see what your results are.
Rule of thumb for me - Always use the largest
nail, staple, or screw you can without going through the other side. Does not apply to attaching things like 1/8"
luan to 2 x 4.
Another rule of thumb -
nail, screw, or staple should be three times the
thickness of the item you are attaching. Once again this is a rule of thumb, it does not apply in all situations.
And yes,
throw away those old screws. The cost of s screw is generally less then a penny and a used one can add hours to a
build or
strike. Aluminum cans are worth more to recycle than screws - recycle your cans and buy new screws.