Start early in the day – Before the sun heats up the land there is usually far less wind, causing blur. Also, there is often dew on the flowers (or frost in winter), which can add another dimension to your pictures.
Photographs in the Sun – Flowers look great in the sun with the naked eye, but neither film nor digital can cope with the increased contrast. Overcast conditions are usually best, colors then saturate and your pictures will still look really bright, but even more colorful. There are exceptions to this though – for example, sunlight can create dark shadows behind your sunlit subject, creating an excellent non-distracting background.  If you are going to take flower pictures in sunlight, try using a polarizing filter to reduce glare and enhance the colors. For best color results, shoot blue or violet flowers early in the morning, yellows in mid-morning or mid-afternoon and reds in late afternoon.   – Place a diffusion screen between the flower you are photographing and the sun. You can completely block the sun and put your flower in shade, then redirect some light back on the flower with a reflector. This reflector can be a commercially made reflector or just something reflective like a white T-shirt or a piece of foam core (also try gold or silver reflectors). Another photographic technique would be to use fill flash.  If your camera has an automatic fill flash function then give it a try.  Experiment with the lighting ratio if your camera will let you change the flash output.  Having the flowers backlit by either the sun or an off-camera flash will brighten and highlight flower petals. 
Use Lower ISO settings on your Digital Camera – To get the lowest noise, (similar to grain in film) most digital cameras work best at ISO 200, so use this setting and a tripod for best results.
Control your depth of field – If you are photographing a single flower with a busy background then use a wide aperture to selectively focus on the flower and blur out the background. Conversely, if you are photographing a field of flowers the use a smaller aperture setting to bring most, if not all the flowers into focus.  If your camera has a depth of field preview then this is the time to use it.  To blur your backgrounds, use a large aperture (small number like f5.6) to avoid distracting backgrounds. Using your camera’s depth of field preview feature is the best way to ensure that you’ve blurred the background – and still got enough of the flower in focus
Spot focus – The normal focus mode of most digital cameras is some sort of average focus mode.  That means that the camera will try to look at an area and base the focus on an area of what it sees.  It’s better for close up photography to put the camera into spot focus mode, this will allow you to see exactly what the camera will be focusing on.
Multiple photographs – Set up your first shot to include the whole flower then concentrate on the details of the flower that attract your eye. Focus on the color or small details of the flower.  Photograph your flowers from different angles. Shoot straight down, from the side, from the underneath, just change it up a little.  Shoot horizontal and vertical.  Position yourself low to the ground to give the perspective of the flowers.  If you kneel or lie down on the same level as the subject, the flowers will appear larger in the photograph, and they will fill up more of the frame. The low perspective also keeps you from shooting the tops of your subjects’ heads and making the flowers look small in the photos.

TECHNICAL STUFF…

Use a tripod – getting close increases the chance of camera shake, so it’s best to use a tripod whenever possible. It also slows down the picture-taking process, which means you have more time to concentrate on the composition
Shoot RAW format files – If you have a camera that will allow you this option. You can only get the most from your pictures by shooting RAW – the highest quality.  For Cameras without RAW File Option, use the highest quality JPEG that your camera allows you to choose. You can usually find this setting somewhere in the menu screens. If your camera has a screen with a histogram (the histogram is the little graph looking thing on the menu screen), always view the screen after your first shot and at the beginning of every series of shots with the same subject. The most computerized matrix meters can’t always get the correct exposure. One of the major advantages with shooting digital: you can see what you have right on the site, and, you can see exactly if you have obtained all of the information available simply by looking at the histogram. A good histogram will have the whole curve within the confines of the box, and not have most of the data up on one side or the other of the box. Especially avoid going over the edge of the right side of the box. That means you have lost the data in the lighter parts of your subject and you can never get it back.
DIGITAL Storage Cards ‘FILM’ – This consists of CF (CompactFlash) or the smaller SD (Secure Digital) cards. These can be used over and over again indefinitely. After you upload your full card to your computer you should ‘Reformat’ the card INSIDE the camera for the next batch as opposed to just deleting the files. Reformatting leads to less storage errors in the future.  CompactFlash cards are basically faster and larger capacity than SD cards.  If you have a choice in your camera, choose CompactFlash. They are priced based on write speed, the faster the more expensive. Write speed isn’t all that important for flower photography. Use multiple cards, because you don’t want all of your eggs in one basket, right? 200 full RAW images per card is a good standard to use.