"By guess and by God" is a colloquial phrase that means to proceed without a well-thought-out plan or strategy. To convey this meaning, similar idioms or phrases can be used, such as "winging it," "going with the flow," "playing it by ear," or "flying by the seat of one's pants." These expressions are often used to describe spontaneous actions or decisions that are made without any previous planning or preparation. They imply a level of risk-taking or improvisation, and while they may sometimes result in positive outcomes, they are also likely to involve uncertainties and potential pitfalls. Choosing the right synonym for "by guess and by God" depends on the context and intended tone of a message or conversation.