As you say, getting the initial curves correct and of good quality is important.
A few important guidelines:
Sketch the problem you are trying to solve not the answer you are thinking about.
For example designing a pen holder I first sketch the pen floating above a plane representing the table, then sketch the maximum size it can be, then the key characteristic shapes.
In mechanical design would not draw the outside profile of a piston rod, just two circles and a line connecting them. Then extrude with offset each of these, boolean, taper an blend until the answer delivers itself.
Use curves to create surfaces or curves to derive a combined curve but do not use derived curves to construct more curves. Go to surfaces when you can.
For example creating bulwark of a mega-yacht I create splines of side view and and of top view, combine then sweep a spline to create a surface along the combine.
Designing a shampoo bottle use splines to create 1x1 studio surface four times to create sides then style blend to round the corners.
Do not define your fillets in curves, build surfaces oversize an use surface blending commands near the end of design.
Hi @Cesare What you share is exactly the kind of case tutorial I need. If you can share its part file, I would be very appreciative. If it's confidential, no problem and I would try to figure it out myself once I get my current project done. Thanks!
I'm very happy to attach you the file.
Here are some explanations.
The first part, the central one, is controlled by four Splines. The external profile is obtained by the Combined Curve Projection command. The points obtained by the Section Curve command are used to construct the two final splines. These spline are the Cross Curve of the Through Curve Mesh. Note that in this Through Curve Mesh I use the same curve as the first and last primary.
The second part, the 'dome', is made by 'automatic' curves like Bridge Curve, Isoparametric Curve and il is made so as to have four-sided patches.
Finally the third part, note as the lateral profile is controlled by the Curve on Surface, surface controlled by a Spline.
Also note how I preferred to mirror the construction curves instead of the surfaces.
The final Through Curve Mesh passes though five Bridge Curve, the first one has p375 and p376 parameters shared with the others.