To be honest there really aren't any reliable ones. What mattered in 2016 led many people to believe Gillum and Nelson would win comfortably based on early returns in 2018 when they led easily in Pinellas County and also had leads in Duval, Seminole, and St. Lucie Counties. It ended up not mattering since they underperformed Clinton a lot in Miami-Dade.
Add in that the early returns this year will probably be heavily Republican-skewed with most Democrats voting by mail, and you just won't have really good indicators.
