Always refer to the directions on the label. For best absorption, some dietary supplements should be taken with food; you may need to take others on an empty stomach. If it is not stated if you should eat before a meal or after, it means it doesn't matter and you can take it any time of the day.
If you forget to take your recommended dosage occasionally, it is fine. Just continue the next day.
If your supplement contains "Caffeine" (e.g. Lean Body Formula/Raspberry Ketone Extreme), we recommend you take them at least 8 hours before your bedtime as it may keep you too active from sleeping.
Like with all supplements, if you have any pre-existing conditions, you should always consult a doctor before taking any health supplements.