Just as a child will eventually string two and then three words together to create a truncated sentence, so too, the child who signs. And just as children learn to speak from hearing the spoken word, so too, children learn to sign from watching their caregivers sign.
The next and most obvious way to begin introducing the notion of putting words together is to use the sign for “more” and then add a noun such as apple or banana.
As you sign these two words together, be sure to also say, “Do you want more apple?” or “Do you want more banana?” so that the children continue to hear a complete sentence (you would not only say the two words “more banana”).
You could also say, “Are you hungry?”
Another way to string two signs together is to add the signs “please” or “thank you”. Modeling these appropriate responses at the appropriate times encourages children to think about feeling grateful. However, I don’t necessarily expect very young children to use these words on their own. Toddlers don’t necessarily feel grateful. They expect that people meet their needs. However that said, I do think they eventually internalize these norms of behavior and will add these gracious additions to their vocabularies.
When putting signs together, do not worry about the little words (i.e., articles) as the goal is to communicate. Try to mimic with signs the way toddlers speak when they are beginning to put words together; “Me, up.” “More apple.” “Done banana.” 2 signs is enough when supporting them with all of the words to complete the thought; “You want me to pick you up?” “You want more apple.” “You are done with the banana.”