First thing you need to decide is how much money you will be working with for the entire wedding.
Then you should follow this guide for a general idea of how much to allocate to each aspect of the wedding.
Here is a general rule of thumb:

45 % - Ceremony & Reception

• Fees
• Ceremony Site
• Officiant (priest etc.)
• Marriage License
• Reception Site
• Rentals
• Photographer's Fee
• Food & Beverages
• Cake
• Bar
• Transportation to and from the Ceremony and Reception for the Couple
• Guest's Transportation and Parking if needed
• Tips Coat Check etc.

10 % - Flowers

• Ceremony Decorations
• Bride's Bouquet
• Maid of Honour and Bridesmaid Bouquets
• Flower Girl Basket and Petals etc
• Corsages
• Boutonnieres
• Reception Centerpieces
• Decorations

10 % - Photographer

• Engagement Portrait
• Photographer's Fees
• Wedding Album
• Parent's Album
• Additional Prints
• Videography

10 % - Wedding attire

• Bride's Dress
• Headpiece and Veil
• Bride's Shoes
• Lingerie
• Jewellery and Accessories
• Hair and Makeup
• Groom's Tuxedo / Suite
• Groom's Shoes
• Groom's Accessories
• Wedding Bands

10 % - Music and other Live Entertainment

• Ceremony Music
• Cocktail-hour Music
• Reception Music
• Live DJ, Musicians, Dancers

15 % - Stationery, Gifts, Favours and other Accessories

• Announcements
• Save the Date Cards
• Invitations and Envelopes
• Bulletins / Programs (Order of Service)
• Seating Cards, Place Cards
• Menu Cards, Thank you Notes
• Favor Cards
• Calligraphy
• Postage
• Guest Book
• Maid of Honour Gift
• Bridesmaid's Gifts
• Bestman's Gifts
• Groomsmen's Gifts
• Child Attendants Gifts
• Bride's Parent's Gifts
• Groom's Parent's Gifts
• Favours
• Ring Pillows

(Courtesy of Weddingstar Budget Planner)