Resistor Notes

Design for E12 (or E6) values wherever possible. They are easy to find, and cheap:
E6: 1.0 1.5 2.2 3.3 4.7 6.8
E12: 1.0 1.2 1.5 1.8 2.2 2.7 3.3 3.9 4.7 5.6 6.8 8.2
Metal-film construction has lower parasitic capacitance and inductance, and generally tighter tolerance (<= 5%) than carbon.
Power rating is typically specified at 70°C ambient and linearly derates to 0 at 150°C
High-power wire-wound resistors have significant inductance; use them appropriately.

Potentiometer quality is often visually evident. Tiny trimmer pots do not hold up to daily use. Heavy panel-mounts do.

Form-Factors
Panel-mount - Often designed to MIL-94 (25,000 rotations), these are most robust.
PCB-Mount with Shaft - Typically designed for occasional use.
PCB-Mount Trimmer - Designed for infrequent use. Not mechanically robust. Use sparingly and carefully.
Construction types
Cermet - Highest heat/power rating, low temperature coefficient. (Prefer these!)
Carbon - High heat/power rating, high temperature coefficient.
Plastic - Low heat/power rating, high temperature coefficient.