The nonfarm payroll report for January will be released at 8:30 a.m. eastern time Friday, and you should consider locking a mortgage rate before then.
According to Briefing.com, the consensus prediction is that the economy grew by a net 148,000 jobs in January. If the nonfarm payrolls number is higher than that, then mortgage rates could go up. If the nonfarm payrolls number is lower, well, I don't know if rates will fall. Rates are low already.
If you're optimistic about the economy, you'll lean toward locking your rate before the jobs report comes out. Today's homebuyers are, almost by definition, bullish on the economy.