1. Book ahead! One thing you must do is give people loads of notice, that way you can ensure everyone you want to be able to make it.
2. Set a theme and tell people about it, ie Chinese dress.
3. Book a catering team if you have many guests
4. If its a garden party rent a small marquee
5. Have some friends play waiters, it makes the evening seem more professional.
6. Have some quiet music in the background
7. Have a retiring area for after coffee, ie a lounge room
8. Have fun yourself, a relaxed host makes guests feel at ease.

I always advise setting a theme as it can make the evening more enjoyable. Maybe have some specials lights..or some men dresses up to greet the ladies at the door.

Always have champagne flying around when guests arrive.

BE aware of people allergies and people being a vegan or vegetarian.

Make it on a weekend so people can let their hair down and also try to make it an event so people feel compelled to go such as your 40th birthday.

Most of all have fun yourself and let your hair down.