I disagree withg faidoi completely: one of the reasons for faster and better bodies and lenses is more accurate and faster auto-focus lock. Mmanual focus is hard to handle without the focussing screen found in the viewfinder of manual SLRs. Auto focus SLRs are made to be used in auto focus mode for most of the time. The autofocus is usually more accurate when used properly than the human eye through a tiny viewfinder.
Focus lock is an important skill to master: get used to aligning one of the focus points on the subject, pressing the button half way to lock the focus, holding the button down while recomposing the shot and completing the press when you have the correct composition. After a while, it is very quick to gain focus lock (more accurate than your eye can be, especially at long focal lengths).
You may wish to lock the focussing ring to one of the nine focal points and get used to always focussing with that one. The central point on the 20d has a very sensitive focussing meter on the centre point when using an aperture below about 5.6 (from memory). It reduduces sensitivity to the same as the other focussing points at smaller apertures.
With the macro, focussing has to be manual. And manual means moving in and out with the body, as well as twiddling the focussing ring.
If you are having real difficulty at long focal lengths, focussing through, say, tall grass, you could try focussing on something that is the same ditance away but easier to target (say a tree), and switch to manual focus then, bwing careful not to knock the focussing ring while recomposing.
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