Ten points to remember or think about:

1. Only collect work you genuinely like - whoever it is by or whatever its price.
2. Don't buy photography as an investment - buy it for pleasure.
3. Specialize in your collection - perhaps on one or two areas of work, or countries or periods.
4. Keep as much as possible of your collection on view in your home or office etc, displayed in suitable frames etc.
5. Never hang photographs in direct sunlight. For older works and some special processes you may need to provide low lighting levels.
6. Use archival materials to store and frame pictures, and try to ensure proper storage conditions.
7. Spend at least as much on living photographers as on dead ones - it is important to keep the medium alive
8. Use the knowledge and experience you gain in collecting to buy work from unknown photographers. If you enjoy the work, back your own judgment and buy it.
9. Always remember that galleries are in the hype business - listen to their advice but trust your own judgment.