Having a party for graduation lets everyone know where you are at and what you will be doing in the future. It is a good way of honoring someone who has made it through school. You can decorate in a big way or you can keep it small with no decorations at all.
Graduation parties could have a theme. A graduation party is about the person or persons who are graduating so you could use that as your theme. Place pictures of the person graduating all around the party area. Make big posters of the person and hang them on the walls. You could start out with a picture of the person as a baby and have pictures of them growing up to where they are now. Make a picture book of all the various things the person has done through the years like the sports they did or the dance classes they took. For table center pieces you can put pictures of the person in a plastic cube or put the pictures right on the table with a clear plastic over them to protect them. You can order a cake with the picture of the person on the top for desert.
A very common theme is the school where the person went. You can make all the decorations in the school colors. Table clothes, banners, napkins, balloons and invitations can all be made out of the school colors.
If the person graduating was very interested in one particular activity you could use that as the theme. For instance if the person was a big member of Future Farmers of America you could do a theme on that. Animals could be all over as decorations. Cows, horses, pigs and chicken pictures could be on the walls, tables, plates and napkins. Have pictures of the person doing the activity and having fun at it.
Most graduation parties have a table or area where the graduate is honored with pictures and uniforms that they wore and any awards they may have won. This area usually has a container of some kind like a box or bag that is for any graduation cards that may be given to the graduate from guests. It is a good idea to decorate this container and make it plain that this container is for graduation cards. This card container needs to be watched carefully since not everyone is the world is trustworthy.
Have some games available for your guests to play like horseshoes, badminton or croquet. Most importantly have a good time and make sure your guests are having fun as well.