two steps ahead

beast with two backs

Two people united in sexual intercourse in the missionary position.

eat for two

To be pregnant

fall between two stools

To fit into neither of two categories and, hence, be neglected or fail.

feed two birds with one scone

Synonym of kill two birds with one stone.

for two pins

Readily, with only the slightest encouragement.

full speed ahead

Maximum effort without reservations or delay.

get ahead of oneself

To focus excessively on one's plans or on prospective future events without paying adequate attention to the present.

greater of two evils

The most harmful or unpleasant of two undesirable alternatives.