problem using manual focus
For manual focus, practice, practice, practice.
Your at a disadvantage if you're trying to manually focus with an AF lens. AF lenses have poor manual focus "action". A real MF lens has a focusing ring that rotates more degrees around than does an AF lens, which will rotate much less from macro to infinity.
Also, MF lenses have a smooth, damped focusing action, whereas AF lenses have too light of a touch to their manual focus ring, with little or no dampening.
Also, MF lenses, using a helicoid focusing mechanism, do not suffer from the clutch "gap" problem that AF lenses have when you reverse your focusing direction. There's always a bit of play when you try and change focusing direction on an AF lens. Some of the higher-end AF-S AF lenses supposedly do not have the clutch gap problem as bad as the cheaper AF lenses.
For example, I once used a Canon EOS 300mm f/2.8 lens which had an excellent (for an AF lens) manual focus ring. But still, the manual focus action felt "detached" compared to the action on a true manual focus lens.