When beginning to get into 3D printing, you may ask what should you look for in designs to better optimize them for the printing process. It is actually quite simple and involves just as much foresight as any design for any manufacturing process. This includes things like knowing your tolerances, evaluating printer limitations, and knowing what material will be used.
Each machine that you will use throughout your experience with 3D printers will print a little differently, even those of the same make and model. They all will have slight variations on each other, though not necessarily significant changes. This is why testing printers before use is important, to evaluate their tolerances as well as to calibrate them to be as accurate as possible. This information that is collected can then be used in your design and understanding of the part. Keeping a part within the printers tolerances is important to ensure no printer errors, which can cause catastrophic failures. Such as a part with too tight of tolerances in an FDM printer could cause the machine to over or under extrude an area and cause the print to fail, or an SLS printer could over melt its powder and cause parts to bow upwards in the print bed and possibly end the entire build. This wastes time and material, and it is best to avoid it at all costs.
It is important to know what the limitations of your printer are too, especially when looking at your printer's process. Key things to take note of include if your chosen printer and process requires supports, and then the environment that your printer exposes your material to. FDM and SLA printers both require support structures to hold a part while it is being constructed, for any areas that are not supported by prior material or are not touching the build plate. This includes all holes and empty spaces within the part. In FDM printers it is also important to note that the prints most commonly will not be 100% solid, but rather have some form of hashed pattern throughout the inside to provide support while using minimal material. More obviously in the printing spectrum is that your design must fit within the build area of your printer. Printers come in many different sizes, from as small as 5x5cm bed size, to several meters in either direction. Keeping a clear understanding of your printer's size is essential to designing a good part.
The last limitation you need to consider is the environment that your printer exposes your design to. Many desktop FDM printers, such as a Makerbot, simply print on a plate exposed to air. This is to help keep the printer simple, and to act as a secondary cooling mechanism to instantly cool the parts once leaving the extruder. This open air concept has an issue however, and parts that are long (8in+ ) in any direction tend to bow upwards due to rapid cooling. While this will not commonly fail any given print, it will produce a warped part that may not be as accurate as you need. The best way to avoid this is to print parts smaller than that on those types of printers, and to use a different type for anything larger. More professional grade FDM printers have controlled environments, where it is constantly heated so that warping does not occur. Plastic SLS printers also abide by this concept and have controlled environments heated to just below the melting point. SLA printers are able to run cold, because they are exposing curing the resin, rather than melting like the other methods. This means that with these printers warping is not as high of a concern.
Finally, when thinking about design with your 3D printed parts, you should consider the material that you will be using. There is a large spectrum of materials that are available to you for printing, most commonly nylon, ABS, or PLA. If you are using PLA or ABS, the likely hood is that you will be using it in a filament form. This means that it will be rounded, and will have limitations for how tight of curves or filets that will be available to you when you are making a part. These materials are used mostly for FDM printing. Nylon is used most commonly in SLS, meaning that it is in a powdered form. This powder will be melted together, and can be easily effected by humidity, the temperature it was stored in, and its age. In regard to design nylon is rather flexible, and is more likely to deform plastically than snap under pressure. This has a broad range of applications in design, from snap fit containers, to catapults. SLA resins vary but are usually proprietary to the maker of the SLA machine you are using. Similar to SLS powder, it can be easily effected by the environment and needs to be stored effectively. Unlike SLS powders however, parts made through SLA tend to be brittle and break easier.
Just like any other manufacturing process, making sure that you consider the tolerances, limitations, and material are the three easy steps to preparing your part for 3D printing.