Are you doing this one square at a time?
For starters, make sure all your squares are the same size and square
I know that sounds very basic, but I had a friend that looked liked she had just hacked out her pieces any old which way. And then she was wondering why they weren't going together very well.
They go together much better when they are the same size and shape.
If your seam allowances are consistent, and all your squares are the same size, it should come out well enough.
Many people sew three pieces in one row, three in another row, and three pieces in a third row. Then press the seams so they alternate from row to row.