Well modelling for 3D printing is as similar as to normal CAD modelling, but like any other machining process you need to decide some degree of tolerance especially when you are designing a parts with int.
Since, modelling can be done on many software, but if you are engineer and want to design a part that have movement so you better understand above statement.
{ Note: I am making a pdf or standard tolerance limit, it is currently under process and will be applicable for all design purpose including for 3D printing. }
So Let me answer how easy is modelling for 3D printing, well it is totally depend on what type of model you are making it can be a simple toy or toy with moving parts, it can be jewelry or any engineering / architecture prototype.
So, if your designing just for basic application I recommend you try online software like ThinkerCAD, Vectary And BlocksCAd. This are the most easiest software that I found for modelling. The best among this that even I use is vectary since its online and can be use to model from anywhere. And also provide all the basic features of modelling.
Other then this the software I prefer are Solidworks, Catia & Fusion 360. Other then this an online software Onshape that you must check out since it helps you to access all yours solidworks model from any device and even edit them.
Well modelling for 3D printing things you need to keep in mind while designing are:
1)Decide the purpose of your design, like what is application?
As you may be aware of that for 3D printing mostly model are save in stl format. In this your model is divided into numbers of triangle and if you use software such as solidwork and try to save as the file in stl format you may get error.
This error is due to very high number of triangle ( this case is mostly with my all models that I had design). But don't worry the solidwork or any other software which such an error will let you save your file n stl format.
2) Now there are special software like meshmixer (which I prefer) which can help you to find the error and repair them.
3) You may have heard the term high Polly or low Polly suraface, well this are the triangular surface that are form while conversion. Now as per your application you need to reduce the Polly surace. The lower the Polly surface the less curve body of product you will get.
4) Well now you may think that you require to model a sculpture where you require high Polly surface, but wait you don't require to reduce the Polly surface almost to 50%, by reducing 5%-10% will also work. After printing you can easily sand the surface and get the finish that you require. This thing are mostly I prefer for FDM printing but if you use DLP / SLA machine this can be avoided since compare to FDM they have very high resolution of printing.
5) Other then Polly surface, things you need to keep in mind are tolerance which i discuss in introduction, if you are designing a part with interlocking joint you need to test print simple joint like hinges to avoid any imperfection in advance model with many joint. It is important to do so is because the part you decide to be moving may not move due to less tolerance provided. If you are working with FDM machine you may heard of retraction, this also need to be adjust by few test print since it vary from model to model and machine to machine.
6) Try to avoid overlapping surfaces while modelling. This may confuse the machine and may leave the area without any material. If you are engineer you may heard that avoid overlapping of surfaces or lines since it may confuse the machine. Well this case also apply to 3D printing since basically its working is similar to CNC machine.
7) Don't make or design the model with layer height below 1 mm. You can design a model say a box with .1 mm but try to avoid for 3D printing. You can 3D print at height but just avoid it since it is of no use.
Other then this if you consider any other basic parameters while modelling please comment below.
THANKS FOR READING!