whatever 3d package you use nowadays, there are still and always will be some rules when it comes down to proper poly modelling. i want to list some reminders you should always be aware of to avoid obstacles.
- keep your faces flat: whenever you move around a vertex, avoid making your face non planar in any way. as soon as there’s more than 15 degrees rise of one vertex to another while the other 3 of a quad are flat, just split your face.
- faces shouldn’t be concave: faces should always be convex. as soon as they become concave, split them.
- don’t make intersections: that seems obvious, but are you sure you didn’t cross over edges by accident which can’t be seen in wireframe mode if you don’t turn on vertex points in the viewport? it’s always worth double checking after an operation.
- never create a non manifold mesh: this phenomenon appears whenever an edge shares two faces. you just can’t make a uvw map which makes sense when you share an edge with seferal faces (which could happen if you extrude an edge)!
- avoid butterflies: nice word for a bad modelling behavior. don’t ever try to connect just one vertex with one vertex of another face. instead assure you always connect at least two vertices.
- no t-junctions: in a perfect topology, there are no t-junctions as they will lead to problems especially when it comes to realtime game engines.
- tris and quads are great: 3 or max 4 vertices per face is just enough. in only the most seldom cases you need 5 vertices to keep your topology in order (e.g. in face modelling, you need one face of 5 vertices on each cheek to retain the topology flows).
and always check in wireframe mode if you can find some unnecessary vertices, double edges or duplicate faces. keep your stuff organized, you’ll profit from it later on. if any operation doesn’t operate as expected, in 99% of all cases it’s a modelling mistake generated by you and not your 3d package going wild.