Without seeing the 3D model, or the pre processing data i can give you some best practice tips for increasing the initial level of quality, and resolution that your 3d maps have.
Always run test flights!!! cant stress this practice enough, it comes down to measure twice cut once; make sure you are finding the best settings for your goals.
1) Fly High - usually over 200 ft is a good starting point, fly a test flight at this height see how the data looks, and than adjust from their. It may seem counter intuitive but in general the higher you fly the better the result will be. This is due to the fact that flying higher will give each photo more data contained in it, that will mean the processing software will have more data to create accurate tie points in a larger quantity. The more tie points the better the ability for the software to determine points in the sparse and dense clouds.
2) Fly Multiple Rounds - One plan will not be enough to create highly detailed models, especially if those models have details, overhangs, and other unique features. I generally fly at least two tiers and usually three when i am mapping with the 3D model as a targeted producible. First fly a mission over the entire area with the camera set straight down, as you might for a 2d ortho. Next you will want to capture some oblique (lower alt but with greater camera angle) this will let you capture details from the sides (an orbit path does quite fine, or you can fly manually) make sure that you dont get too much horizon in these as that can make the tie point processes less accurate. Third i fly a lower mission with the camera almost straight on, especially if the target being mapped has a lot of detail this will help.
3) Ensure a good level of side, and overlap on all tiers of your flights. There is a balance here between detail, and diminishing returns (eventually with say 99% overlap you will see less return as the number of photos increases but the new data in them does not)
4) Time Of Day and conditions - Shadows are generally not good for your accuracy, so shooting very early or very late when shadows tend to be the longest will usually give poorer quality results. i try to shoot around mid day and overcast conditions help minimize the effects of shadows as well.
Post process - even with the settigns correct, the perfect light conditions and multiple tiered flights, the 3d models will not be perfect, you may have to put them into a CAD, or modeling program to close gaps, or tweak the model (especially if a goal is 3d printing)
Hope this helps!!!!
please show us your maps!