Some general tips are to bet as much as the most bettor if you are in the lead with the most chips and bet against the chip leader if you are behind in the number of chips. You should also withhold a chip when everyone else moves all-in.
“Wonging” is a card counting technique developed by university professor and professional blackjack player John Ferguson, who goes by the pen name Stanford Wong. According to this technique, you should watch and count the table without playing and only fill in when conditions are favorable. Some tables prohibit new players from getting involved in the middle of a game, especially because of this technique.
It is relatively rare, but certain blackjack tables allow the away from the table to bet with the other players involved. This practice is more common in smaller casinos that have more demand for blackjack games than they have available table space. Online casinos are rarely bothered by this, as theoretically an infinite number of players can be accommodated at any time.
When piggybacking is allowed, the non-seated players don’t make decisions about how the hand is played, but they usually have the option to decide independently whether to split or double if the player does. This gives teams of players the opportunity to take advantage of certain hands to reduce the house edge. However, the casinos usually prohibit this practice and will kick anyone they suspect.
Aside from the piggyback examples mentioned above, no, not at all.
