Doug,

1. Square knot: simple, strong, easily tied.

2. Two half hitches: a useful slip knot, easily tied.

3. Bowline: a good stable loop, not that hard to tie.

4. Taut line: very useful to tighten tent & other guy ropes.

5. Sheetbend: a wonderful splicing knot. I know you only asked for 4, but this is an old favorite to which I frequently resort.

Good luck,

John