First time TTC tips

I have a DD age 3.  She was pretty much an "unplanned surprise" with an awful bf who became a deadbeat dad.  An awkward situation but I wouldn't trade her for the world!
Now I'm married and DH wants to try for our own.  So of course, I've downloaded this app.  Any of you have tips for a first-timer to increase her chances?  I have no idea what to expect other than just ... you know, doing it.