Use mirror lock-up if you can. Check DOF on depth of field preview if your camera has it. Also, search on-line for details of hyperfocal focussing techniques, this will probably make the biggest difference.
Another factor is using too small an apeture, which increases overall DOF, but also decreases overall sharpness as you begin to suffer from interference from diffraction. (Again - search on sites such as luminous landscape for technical details.)
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