There are two main types of compounds in BSL - those that combine two signs sequentially, often creating an abstract new meaning (and often using arbitrary signs), and those that combine two signs simultaneously, often creating a more visually motivated sign.
Sequential BSL compounds (e.g. SAY+SORRY=FORGIVE or THINK+TRUE=BELIEVE) are often creations that have come in some way from a wish to represent a concept used in English. Also many compounds borrowed from English by loan translation are sequential compounds because they are sequential in English.
Simultaneous compounds such as PLANE+ROCKET=SPACE-SHUTTLE or PHONE+TYPE=MINICOM are more often visual creations.