If the maker is not present, ask that your comments be conveyed. Don't offer help unless there is some expression of interest in actually doing so. For example, if the maker points out the problems, feel free to respond with suggestions or resources but if they show you the piece with pride and a smile. Thank people for teaching, decorating, or otherwise applying their artistic skills at an event. Praise people for trying new skills or improving old ones.
Many people are embarrassed and awkward about receiving praise.
Ask people for their help at some art or science-related task. People like to have their skills remembered along with their names. Be delighted in all the arts and sciences you see around you and share that delight wherever you go. One of the most frustrating and intimidating things you might have to do in your office is to provide constructive criticism on an individual's work or deal with someone who discourages an individual's efforts repeatedly. Positive criticism' is critiquing based on fact or educated guesses.