Formative assessments are very helping in keeping students motivated and on track and are solid indicators of a students' mastery of the content and progress towards the learning goals. 

Gamification is a great way to motivate students and provide a clear path towards buliding both types of motivation. 

It's important that adult learner's feel confidence in their abilities to be successful early in the course to increase their perception of success in the long term. Giving short tasks that build success early on can increase motivation.