Heuristic Evaluation is where a small group of people evaluate a tool based on basic best practices for all applications, not just those in biology/genomics. This is a great first step because it only takes an hour, it doesn't require you to find potential users of your tool (anyone who uses the web will do), and it will catch many of the biggest usability bugs. This will mean that if/when you talk to your users/potential users, they will be finding usability issues specific to your tool's application, rather than just general usability issues.
To set up a Heuristic Evaluation, gather a group of 2-5 people who uses either the command line, if your tool is a command line tool, or uses the web, if your tool is a web tool. Give them some motivation for who they are pretending to be along with a specific 5-minute-only task to complete. Have them fill out the evaluation form below as they go through the task. After 45 minutes have everyone come back together to discuss and summarize any findings.