Scaling up vs. maintaining risk when trades are working

Been trading $MSFT and $GOOGL small for a few months, finally seeing some consistency in my setups, but it's on micro-lots. I'm hitting targets, managing stops tight, but the p/l is still basically beer money. My question is, how do you guys decide when to actually increase your risk per trade? Is it purely a percentage of account growth, or do you wait until you've hit a certain number of profitable trades in a row? I'm worried about getting overconfident and giving back profits when I size up. Any rules of thumb or things to watch out for when trying to transition from 'proving it' to 'actually making something'?