Hiya - if you can lock the focus, then just move slightly back/forth until the focus is precisely where you want it
I find tripods bothersome to set up exactly for that reason, so I find it easier to brace myself against a wall or sit on a chair with my elbows on my knees
If you can't lock focus, focus just in front of your chosen ideal spot - the depth of field will extend to just behind where you focus and with a bit of practice you can judge the depth of field to exactly match the front and back of the subject
Zoom in to focus, then zoom out to frame the image will also improve accuracy, and always use flash where possible to sharpen the image, usually about 1/250 exp or less
Hope that makes sense