Be aware of foods to avoid and don't be shy to check with your GP about any activities you're unsure of. Pregnancy is often when women really take control to properly balance their diet for the first time, cutting out alcohol and taking recommended supplements such as folic acid and vitamin D. Discover recipe ideas at firststepsnutrition.org.
Biding your time
If you have a wide social circle with multiple commitments and need to cancel some dates over a short period, no one is likely to be that shocked. Pulling out of things because you're not feeling 100% won't be a lie.
Desk jobs are ideal if you just need to sit and work quietly while nauseous. You won't be seen as withdrawn for long. If you are in a very mobile or demanding position you may need to confide in your boss who by law is expected to protect you in confidence.
Coping with the unexpected
Your sense of smell can dramatically heighten during pregnancy so be wary of smells you normally find unsavoury. You may also be suffering less glamorous side effects such as constipation and a need to urinate more frequently. For help with screening issues, Antenatal Results & Choices is a small compassionate charity offering huge support and can put you in touch with women in similar situations.