When you don't have a lemon squeezer or juice extractor try these methods for extracting juice. They will work better if you knead and soften the citrus first.
Insert a large fork into the centre of a cut orange or lemon, then squeeze the fruit against the fork to extract the juice.
Gently squeeze cut citrus fruit over an inverted cup, using a saucer to catch the juice. Use an old, valueless cup. (A demitasse cup works best for lemons.)