Pretty simple... use the genderings of anonymous people as a guide.
If anonymous people are calling you by female pronouns more often than not, then you should probably be using the women's room. If anonymous people are calling you by male pronouns more often than not, then you should probably be using the men's room.
And yeah, I pretty much used this as a guide, and had no problems.
About 7 months into hormones, I started being gendered female consistently while wearing a wig, and as such I started using the women's room when I was out in "girl mode." No problems. I kept using the men's room when not in "girl mode," mainly at work, for another 7 months after that. Near the end of that time, I had several instances where guys in the bathroom were giving me weird looks while I was at the sink doing my hair, hiding themselves in shock when I walked into the bathroom. Near the same time, I started getting called "she" pretty consistently, at least several times a day, by customers who didn't know me. At that point, I started dressing more femme with confidence, started using the women's room 100% of the time, and the rest is history, I had no problems at all.