Once you get your model, locate any lingering supports/sprues, and remove them. This can be easily removed using a set of snips or break them using another tool.
Using a sanding stick file any raised areas from the sprues.
Next clean the items with Isopropyl alcohol (IPA) 90% or higher. You can spray or dunk the item in the IPA If there are difficult spots you can use a soft toothbrush and rinse with more IPA. Once the model is clean allow the item to fully dry. be careful not to soak them for more than a few minutes as the IPA can affect the printed model.
If your model requires additional detail parts, please add them at this time. IPA will dissolve the glue. (Not all models require this step)
Once your model is complete you can paint and decal as you desire. I would highly suggest using an airbrush.