What are the little details to not forget when planning an awesome party?

China markers or sharpies for people to write their names or initials on their glass. 

Care that both smokers and non-smokers can be comfortable. Is there an area where smokers can enjoy a smoke without driving away your non-smoking guests? If you're a smoker yourself, you find it hard to believe how unbearable some smokers find being around smoking. 

Hide any valuables like jewelry, prescription drugs. 

After party card games.

China markers or sharpies for people to write their names or initials on their glass. 

Care that both smokers and non-smokers can be comfortable. Is there an area where smokers can enjoy a smoke without driving away your non-smoking guests? If you're a smoker yourself, you find it hard to believe how unbearable some smokers find being around smoking. 

Hide any valuables like jewelry, prescription drugs. 

parking for starters.Music.... which rooms is off limit..Decorations..Napkins

Cups

Plates: For both mains and enough for cake

Table Runner or Tablecloth

Cutlery: Knives, spoons, forks..Party Food: Sausage rolls, sandwiches, popcorn, mini-burgers, mini-pizzas, mini-quiches, mini-pies, hot chips, frankfurters, chicken or fish pieces, macaroni, parfait, hot dogs, brownies, chocolate crackles, muffins, ice cream, waffles, pancakes, jelly cups.

The Cake: Of course! You can make one yourself or get one made ahead of time by a bakery or cake shop.

Ice: Either buy a bag or make your own ahead of time

Drinks: Preferably a variety for different ages and tastes. Some ideas include kid’s PopTops, poppers, mixed drinks, cans, water, tea, coffee.

Games & Activities

Music and a portable CD player

This is the one for your parents, right?

Organize people to help you with certain tasks.  Many hands make light work and all that.  This is especially important for the clean up.

Clean the house a few days before the party.  Remove ornaments and excess decorative cushions.  These can easily get knocked over when a house is crowded and people will need space to rest their plates and drinks.

Make sure there is plenty of soap and toilet paper in the bathrooms and that each bathroom has a waste paper basket.  While you're at it you may want to make sure there's painkillers, Sudafed, TUMS, and the like available just in case.

Reserve a room for people to put their coats.  This is usually a bedroom.

If there will be a lot of young cousins set up a room as a playroom as grown up parties can get a little overwhelming/boring for children and young teens.  Stick some board games in there so cousins can play together and not all be absorbed on screens.

Know where the cleaning stuff is and make sure it's accessible.  Have plenty of paper towels and maybe some carpet cleaner.  Someone will drop something at some point.  It's best to clean up before anyone treads in it.

In the days before the party use up the contents of the fridge to make more space.  Work out if you need coolers and ice.

If you want the trash to be recycled have sorting bins or bags somewhere like the garage or laundry room to make it easy to sort as you throw away.  Put signs next to them if it helps.

Make sure you have enough chairs.  If it's your parents 25th anniversary I can guess that there will be many guests who are uncomfortable standing for long periods of time.  They may circulate but they'll want a rest every so often.

If you're serving alcohol people tend to get peckish as the evening wears on.  You don't have to serve all the nibbles at once.  You can hold some back for the second half of the evening.  Make sure there are plenty of soft drinks too.  Even drinkers want to space their beverages.  Have coffee for the end if the evening, hot cocoa for the kids.

Choose music everyone will at least not mind.  Classic top 40 radio collections are made for this type of event.  Double points if you can get a mix from the year your parents got married.  Keep the music at a volume people can still talk over (unless everyone agrees to get up and dance).  Hint, hint, the macarena was the dance everyone hate-loved in the mid 90s.

Check the trash for cutlery before you tie up the bags!

Guests want food, drink, parking, a reasonably comfortable place to sit and a place to put their coat.  

It's amazing how many events I've been to where there was no place to park, sit or even though there was food, they ran out of plates or cups.  

Make sure you've got the basics well covered before sweating the small stuff.

Balloon's???