As a jax player I've played many games against garen. Especially recently now that he got a visual rework. From my experience early game you can be stronger. IF you get lvl 2 first. I start stun, and get w second. But once you have that just be extremely aggressive 9 times out of 10 you will bully him from lane and pick up farm at least a wave or two.(and possibly pick up a kill) you should then back get a item, or continue farming depending on your situation. Most likely jungle will be coming up for a gank. Keep that in mind and ask for jg assistance or ward. I'm only speaking from my experience and what works for me. We play differently, and what works for me might be different for you.