Close-up: Working in the Field
By now you've probably come to learn that macro photography can be both challenging and rewarding. At home or in the studio, the wind doesn't blow and you can plug in as many extra lights as you need. The floor is unlikely to be muddy. When shooting in the field though, you have much less control.
The first thing you need to do is to take your time and don't feel rushed. Think things through and plan what you are going to do.
Tripod position can be critical. Even a slight difference in position can alter your composition considerably and change the plane of focus to emphasize different parts of your subject. To be able to shoot as low as possible, get a tripod without a center column. To get really low though with any tripod, lay it on its side. Splay out two of the legs so they form a "V" on the ground. Now tilt the tripod head up to re-level it to create a base to mount your camera on. This can take a bit of practice isn't likely to be as stable as setting the tripod up the normal way, but it sure works well in a pinch. A focusing rail or macro slider can be quite useful to fine-tune your position.
Wind is a frequent adversary. Even a light wind can move things enough to make shutter speed a major consideration when you'd prefer to go for depth of field. Sometimes fill flash is the answer, but try blocking the wind first. Merely placing your own body or camera bag on the windward side of your subject will often do the trick if the wind is mild. Patience, too, can be a virtue. Even when the wind is stronger there will usually be lulls enough to get the shot. You may have a fair number of shots spoiled by sudden gusts you didn't predict, but keep at it and your efforts will frequently be rewarded. Wind is often less of an issue early in the day too so the answer may just be to come back at a different time.
You may find it helpful to actually lie down on the ground when practical. You can use a large plastic trash bag as a ground cloth to avoid getting too messy. A right-angle viewfinder attachment can be quite helpful as well.
Sometimes a shot can be improved by "grooming" the scene a bit. Nature can be beautiful, but it can also often be cluttered. Loose twigs and such are easy to pick up and can make for a much more compelling shot, but don't go overboard. As with wildlife shooting, no photograph is worth endangering the welfare of your subject. Don't pull up living plants or move things around to create something that couldn't have been naturally on a good day. As an alternative, try gently bending plant stems over and holding them down with something convenient. Small rocks or sticks, the ballpoint pen or car keys in your pocket, a lens or extension tube you aren't using or most anything else at hand will serve the purpose. Don't break any live stems, but with care you can get most small obstructions out of your way long enough to get the shot you want.
One final note: keep track of what equipment you take out of your camera bag so you can be sure not to leave any of it behind when you get up.