BBT tips and Preseed question

Been ttc for 10 months now, had a chemical in March and have been trying ever since with no luck. So this month I’ve decided to track my bbt. I’ve never tracked my bbt before so I could use some great advice from you ladies!! I also am thinking about buying preseed again which I used the cycle I got pregnant but have heard so many horror stories about it causing chemical pregnancies and after getting pregnant using it and then having a chemical myself, I’m a little skeptical about using it again.