I really like Kaye Wood's tips and techniques. Here she demonstrates her method of doing a Y seam. I used this making a quilt that had tons of Y seams in it and it worked like a charm.
https://www.youtube.com/watch?v=XLkHfcuNzCA
She has lots of other tips on being accurate as well.
To get my points to be pointy in a pattern (like in triangles, stars etc) I put a pin through the point and then through the fabric I'm sewing it to. Most of the time it is 1/4" but not always as often there is just enough give in fabric to be a little off at that intersection. I make a mark on my fabric that I'm sewing the point to with a Frixon pen where the pin comes through and that is my seam guide when I go to sew my pieces together. Perfect points every time. Even if the seam on the backside isn't perfect who will notice.