One thing that can be manipulated to increase
'depth of field' (what is in focus) for any lens
is increasing the ISO sensitivity which allows
a smaller lens opening (higher F stop number).
Using ISO-1600 works well for me usually.
Another trick is using your 'depth of field'
button which stops the lens down to the smallest
pre-set opening to give a check on focus range
(if it has this feature). You may have to use an
apeture priority mode on camera for this. IMO the
auto exposure mode on digital gear seems to bias
towards high shutter speeds reducing the focus range.
In general, a wide angle lens has greater depth of
focus than a telephoto. My digitals in macro mode
reduce the number of focus points to 'one' which
cam be a problem if you don't want fuzzy backgrounds.
If the above stuff was mentioned previously, it was
just missed scanning the posts. A local photo club
could be helpful too; the local here deals with more
techniques for close-up, lighting & calibrating your
computer monitor to printer, etc., and experience
with members gear beyond your own.