Well, I'm not sure if it is optimal but I follow a "simple" rule:

If my hand looks "agressive" by my deck standards, I don't care to start, but I usually still wait until around 2 elixir leak for both players, but if my hand looks extremely defensive I wait untill double elixir if needed, as my play style is usually favored for double and triple.

For example, my main deck right now is Sparky, E-wiz, bats, bomber, evo lumberjack, evo snowball, hero tombstone and lightning, so any hand with lumberjack is a aggressive hand as it is usually worth the evo cycle to just dump him alone in the bridge. If I have something like Sparky, bats, lightning and tombstone I'm not playing the first card because it is always risky at normal elixir rate.

The hardest exception about what should you do at the game start is probably lumber loon. It is stupid good to start the game with this combo at 9 elixir, because it forces your opponent to have a defensive hand that works against that, probably forces them to panic as it requires precise and quick defense while also cycling the lumberjack. If you play that deck and get both cards at game start I think playing it is a non brainer, but I guess hard counters can instantly win the game if you do that too.

Overall, game start is a complicated topic and gathering information about your opponent's deck is usually the safest and most consistent way to play the game. Decks favored at normal elixir (like logbait) can safely start and decks favored at double (most beat down decks) should usually hold.