You've decided once and for all to deal with those melamine kitchen cabinets, update the master bedroom or add another 300 square feet of living space. You've hired a pro to help with the design and now it's ready, set, go! But before you go shopping for fabrics, finishes, art and paint, we've asked the experts to weigh in with some design dos and don'ts that'll help you avoid blunders that are beyond repair.

Blunder #1: Not formulating a budget
Bill Adler has been designing spaces for more than 25 years and the majority of his work, through William L Adler and Associates Limited, is residential. Bill recalls a client who was doing an extensive home decor renovation. "We went through the home area by area and we came up with a budget of $95,000 to $125,000," he says. Bill used that budget to solicit contractors and found someone willing to do the work. "Then the homeowners said 'we only want to spend $50,000.' " No problem. "We'll just lop off half the project," Bill told them. But no -- that's not what the couple had in mind. "They wanted all of it, but for $50,000," he says. Of course, that was impossible and became an enormous headache for everyone involved. Be certain of your budget (and your limitations!) before you agree to anything.

(Discover how to stretch your decorating dollars.)

Blunder #2: Accessory overkill
"There seems to be a general feeling that if one accent piece is good, 10 are better," says Sue Bennett of Bennett Design Associates in Uxbridge, Ont. Wrong! "Stick to the KISS principal -- keep it simple and stop," she advises. Display single items of larger pieces or groups of three for smaller ones, otherwise you create a "cluster of confusion," she says. "If you're creating a theme room around an item -- like birdhouses, for example -- find one wall to display them on and then stop." That means no birdhouse patterned throw cushions, or birdhouse-themed wallpaper.

Blunder #3: Being afraid to make a statement
Everyone wants to personalize their space, but they're afraid, says Bill. "'If we paint the walls green, we'll never be able to sell the house,' they say. I ask when they are planning to sell and they say, 'Not now, but maybe in 15 years.' By that time they'll have painted three times over," says Bill. On the flip side, if you really are planning to move in a couple years, your focus should lean more toward "dolly dress up," as Adler calls it. "You probably shouldn't spend $60,000 on the kitchen and $30,000 on the powder room if someone else will have it in a year."

Blunder #4: Choosing form over function
Some details and fixtures are gorgeous, but simply don't fit your lifestyle. For example, hardwood on the kitchen floor. "It sounds lovely, but if you have three kids, two dogs and a cat, it's not for you," says Bill. All that running back and forth will mean many expensive and inconvenient bouts of refinishing. "And if the dishwasher overflows, the floors are toast," he adds. Bill advises people to consider practical and beautiful alternatives besides tile: cork and rubber, the kind used on basketball courts and in nursery schools, are two choices he recommends.

(Read our Buying guide: 11 flooring options for more flooring ideas.)

Blunder #5: Forgetting lighting
"Choosing the wrong lighting for a room can ruin the ambiance," says Sue. "For a room that you'll be working in -- like a kitchen or office -- you require task lighting." That can take the form of valance lighting under kitchen cabinets, an adjustable-arm desk lamp, or even a gooseneck standing lamp for needlepoint work. "Task lighting is always used in conjunction with the overall room lighting -- whether that's ceiling pot light fixtures, or just a flush mounted ceiling fixture," she says. For sitting rooms and relaxing space, you need ambient light. Sue suggests incandescent table or floor lamps, soft overhead wall washing or dimmed pot lights. "To add interest, be sure you allow for small pockets of brighter light," says Sue. "That can be achieved with accent lights over artwork, or by backlighting or uplighting plants."  Get more lighting ideas!