The formulation and order of integration used in a continuum element can have a very significant effect on the accuracy and cost of the analysis.
First-order (linear) elements using full integration are prone to shear locking and normally should not be used.
First-order, reduced-integration elements are prone to hourglassing; sufficient mesh refinement minimizes this problem.
When using first-order, reduced-integration elements in a simulation where bending deformation will occur, use at least four elements through the thickness.
Hourglassing is rarely a problem in second-order, reduced-integration elements. You should consider using these elements for most general applications when there is no contact.
The accuracy of incompatible mode elements is strongly influenced by the amount of element distortion.
The numerical accuracy of the results depends on the mesh that has been used. Ideally a mesh refinement study should be carried out to ensure that the mesh provides a unique solution to the problem. However, remember that using a converged mesh does not ensure that the results from the finite element simulation will match the actual behavior of the physical problem: that also depends on other approximations and idealizations in the model.
In general, refine the mesh mainly in regions where you want accurate results; a finer mesh is required to predict accurate stresses than is needed to calculate accurate displacements.
Advanced features such as submodeling are available in ABAQUS to help you to obtain useful results for complex simulations.