A birthday party is always festive - the mere presence of a guest of honor and a towering layer cake are all you need to set the tone. But why stop there? There are so many ways to make these celebrations even more special.

Any party gets a sense of focus and excitement from a theme, which influences everything from the invitations to the menu to the decorations and activities. Both children and adults can have a good time with a theme, making this kind of party excellent for birthdays, which are often gatherings of family and friends of all ages. Crowd-pleasing parties include: a sock hop (play music from the '50s and have a limbo contest), a luau (offer fresh-flower leis to guests as they arrive, and illuminate the backyard or the beach with tiki torches), a square dance (borrow a friend's barn, and hire a caller), a clambake (substitute a raw bar and grilled lobster for the traditional barbecue pit on the beach) and a Mexican fiesta (serve dishes such as guacamole and quesadillas, and use pinatas as decorations).Or just let the birthday be the theme. Update a classic children's party, making it elegant enough for an adult guest of honor. Here are some ideas:

- Set the table with beautiful linens. Along the center of the table, alternate small, lush arrangements of flowers and little bowls or cups of noisemakers.

Buy helium balloons in just one or two colors that complement the table setting (you can find them at card shops and party-supply shops). For an outdoor party, anchor the strings with stones or bricks on the ground, creating a circle of balloons around the table, or dot them across the lawn. For an indoor party, remove the strings and let the balloons float to the ceiling over the table.

- Have a homemade party hat waiting for each guest.

Use medium-stiff art paper in favorite colors or simple patterns. To make a cone-shape hat, cut the paper into a 12-inch square, tack a length of string (about 14 inches) to one corner, and tie a pencil to the other end, creating a makeshift compass: Extend the string to draw an arc from one corner of the paper to one opposite. Cut along this line, roll the paper into a cone, and glue or tape to secure. Punch a hole or cut a small slit on either side for ribbon ties - and make sure you use the prettiest ribbon you can find. I like polka-dot and gingham grosgrain ribbons with solid-color hats.

- For goody bags, fill the bottom of clear cellophane bags with penny candies or jellybeans to weight them, and add little gifts, such as bottles of bubbles wrapped in tissue paper. Cinch the tops of the bags with ribbon, add name tags and use them as place cards.

- Create a birthday card that will become a keepsake. Make a color photocopy of an old picture of the guest of honor, and use photo corners to attach it to the front of a simple folded card of stiff paper. Write a birthday message below it, and - most important - be sure that every guest signs it.

- Have a Polaroid camera and several rolls of film on hand, so you can send everyone home with a picture or two. Or pass out disposable cameras for the guests to use. Collect the cameras at the end of the party, develop the film and send guests copies of the best photos.

- Plan activities that the whole group will enjoy, such as a softball or volleyball game. Or orchestrate an old-fashioned scavenger hunt.

- Prepare a special drink for both adults and children. For example, sprinkle sweet, juicy cherries (pit them first) with a little sugar, and crush them slightly with the back of spoon. Add a few cherries to flutes of sparking wine or tumblers of fresh lemonade.

The rest of the menu can be as casual or formal as you like - a perfect hamburger is as much of a treat as grilled lobster. Just serve the foods you love to make or the ones the guest of honor loves to eat.

- For dessert, what else but cake and ice cream? Cupcakes are great for a big group, and they make an impressive presentation when you use them to convey a birthday message: Coat them all with icing, then pipe on individual letters, so together they spell out "Happy Birthday to . . . " Additional cupcakes can be decorated with fresh berries; arrange them all in a grid on the dessert buffet.

And here's a new way to serve the ice cream: Remove pint containers from the freezer, and let stand for one minute. Take off the lids, then slide a thin knife or icing spatula between the ice cream and containers, all the way around. Place a plate or shallow bowl on top, invert, and lift off the containers.

Topped with a few berries, the ice-cream towers are pretty enough to be displayed on the dessert buffet - but not for long, of course; scoop the ice cream onto plates of cake before it melts.