I sew lots of tiny quilts. There is absolutely NO room for error. A few things that I do to be successful are using 60 wt YLI soft touch thread. It is cotton and incredibly thin. I starch or size my fabric and use a ruler with 1/8 inch markings for accuracy. These things all help me a lot. Press seams open as well.
Don't be too hard on yourself with these tiny ones. I sometimes think that my blocks look great until I start putting them together.....that is MY test of perfection. I still think my crooked, slightly wonky tiny quilts look charming overall.