The biggest mistake a SaaS company can make is not being data driven. There are some pretty basic things you should be measuring when it comes to user acquisition:

• Unique Visitors Traffic (not just vanity traffic from overall site hits);
• Conversion of Unique Visitors to signups;
• Week over week growth in unique visitors, signups, etc;
• Source performance (traffic from paid and unpaid sources - this will come in useful for measuring the Return On Investment on your marketing campaign);
• Engagement metrics (amount of time using product);
• Set clear targets and goals based on your traffic

Use the "Website Metrics" sheet of the workbook to help calculate this.