If you really want 200 people at your wedding but there is only enough room for 150, have your guest list split in two. A List and B List
Step2
Have 150 people on your A List - The A List contains those people who absolutely HAVE to be there, YOU WANT them to be there. (i.e. Parents, Grandparents etc)
Have the remaining 50 people on your B List -The B List contains those people who you would like to come to your wedding but they don't necessarily HAVE to be there. (i.e. friends, co-workers)
Step3
It's usually a given that 80% of 100 will show which will give you more room so you can invite those off of the B List.
Send them out, once you start getting back RSVP cards that have regrets about not being able to make it, start sending out those B Listers
Tips & Warnings
Make sure you have the most important people on the A List.
Do NOT tell anyone they are a B Lister, it may hurt feelings.
The chances of 100 percent of your guests attending is slim to none but please keep in mind that it may happen