how to focus sharp with the canon G6

I am using the Canon G6 for 8 month and shot a 3000 pictures most outdoors in gardens. In the auto-mode it is almost not possible to focus sharp on a detail like the stem of a flower. In the Av-mode you can use the macro manual focus but even then it gives very often problems to get the picture sharp.
Are there rules to follow to get always the most sharp photo?

Har-
I'm sorry no one answered your post. I hope you see this.

I almost never use auto modes, specifically because they are so poor at doing technical things like fine focusing. I almost always use auto focus, though. We actually have a G6 for our office camera so I have a fair amount of experience with it. Plus, I have a G2 that I used to use a lot. The truth is, the rules are pretty much the same for most cameras, though.

Your example - focusing on a flower stem - is a tough one. The smaller a portion of the frame you need to focus on, the harder it will be for the camera's auto focus. Depending on the specific situation, manual focus might be your best bet. Another thing you can try is focusing on something larger, at the same distance, and recomposing. That's what I would do. I might also switch the camera to manual focus after I got the camera focused. That would effectively lock the focus so I wouldn't have to worry about refocusing.

I hope that answers your question and helps you get better photos. If this is a problem you run into a lot then you might be ready for a digital SLR. Digital SLRs generally have finer, more accurate auto focus.