1. Be clear and specific about what you want them to do. Most Americans will find it de-motivating to have to guess what their superior expects of them. They have been taught from childhood to focus on explicit directions over context-based implicit guidelines or instructions. Although they do also pay attention to nonverbal communication, they may not know how to interpret yours and not expect that important information would not be delivered explicitly. In addition, they don't want to waste the company's time by working on something that wasn't requested.
2. Challenge them, but keep the target realistic. Most Americans like challenges, but if it's not an attainable goal they feel defeated. Achieving goals is one way that they know they are on the right track. While Japanese might be motivated by being told "We should try harder," Americans like to work hard toward a goal, be congratulated for succeeding, celebrate that success, and feel appreciated for their hard work. Then they are ready to set the next goal. "You should try even harder" sounds like "You failed!" to American ears.
3. Let them work independently if they want. Americans don't have a ho-ren-so mentality. They want some freedom in their work and can easily feel like they are being micro-managed if you check up on them too often. An alternative is to explain how ho-ren-so works and the value of it in a Japanese company. Then agree on a schedule for updating you.
4. Give them balanced feedback. Americans would like to hear explicitly how they are doing. They are greatly encouraged by positive feedback. Negative feedback is helpful, but it is important to balance that with positive feedback. If someone has done a good job, it's important to say so. If they haven't, tell them explicitly how it could be better, but do so without scolding or demeaning them. What is considered good or the correct way to do something in one culture may be considered insufficient or the incorrect way in another. Don't assume they are not capable or are lazy, they just may not know what you are expecting.
5. Respect their personal needs. In the United States, it's common for both parents to work and for both parents to play an equal role in parenting. It's important that they have time to attend to family needs, but it's equally important that they have time to provide emotional support to their family. This may mean getting off work in time to attend a soccer game or taking time off when a baby is born.