A strong mentor while in an internship position is vital to learning and growing in a work environment. This is especially true in a startup as many of the processes are being tweaked or reworked every day. A strong mentor can give good advice and tips, while at the same time expecting a lot from the mentee. This is the perfect dynamic for growth.
Because I have built a level of trust with my manager, I am able to work autonomously most of the day and work on what I want to. This is because he set clear expectations about what I was supposed to accomplish each day, each week, each month, and by the end of the internship. It is a sales position so it may have more goals than the average internship. Regardless, having a mentor that sets clear expectations helps the trust-building process speed up because it is easier for an intern to start excelling early. Also because I am trusted to work autonomously, I am encouraged to take on a project and work on it any way I chose as long as it achieves the outcome they are looking for. This gives daily work an extra layer of creativity that makes working more exciting.
The next part of a strong mentor is the ability to ask questions. Asking questions is one of those things that can be done wrong, and it is important to learn not to ask questions that can be time-wasters, ie, anything that can be answered with the internet. So, this forces me to do a bit of research before asking a question, and typically, prevents me from needing to ask a question at all.