Good first leads in sheepshead
I play a lot of dopplekopf (aka double sheepshead although there are more differences than just the deck size). 

A bare fail-suit (non-trump) Ace has a reasonable chance of taking a trick and certainly helps your team. The odds that your partner(s) had a better legal play had they known you were on their team are small, so this seems like a good lead.

If you're the picker's partner, leading a jack (or sub-10 diamond, though jacks are better) to your partner's presumed high trump is a very good play. If you're the picker, consider leading a red queen early to attempt to force opponents into difficult decisions (especially before partners are known).

Leads that might fish out partners are generally more valuable if you have a strong hand (trump) or a lot of points (especially in fail suits), because in both those situations, your hand will be vastly improved by good teamwork. If you have a more middling / balanced hand, letting things go unknown for longer may result in teammates overtrumping each other.