T-Spline surface self-intersects
Model 50% - 80% in box view mode. Check the shape in smooth view mode and make small adjustments. Check back in ox view mode.
Start with as few polygons as you can get away with and only add more detail when you are satisfied with the overall shape. The mode polygons you have in the design the more difficult it will become to make adjustments to the overall shape.
When you need to stretch polygons too much to create a certain shape you need more polygons (create edges and edge loops). The box shape should approximate and resemble the final smooth shape.
Avoid triangles at all cost! Even the most experienced modelers very rarely use triangles and know exactly when they can get away with it. Limit the use of N-gons( polygons with more then 4 vertices/edges) an occasional 5-seded N-gon is fine, but completely avoid N-gons with more then 5 vertices/edges!
Binge watch Arrimus 3d's youtube channel.
He uses 3DS Max and Blender. Different tool sets, but most of the modeling concepts are directly applicable to T-Spline modeling.
These tutorials from namenotimportant are good as well:
