I did a few hours to get totally comfortable in the aircraft. Plan a few cross countries, push yourself a little bit, but always try and get a briefing and get good weather info. Don't go if the weather is looking iffy. Have a Plan B and Plan C!
Then when you are getting really happy/ bored by doing that, why not get checked out on a "complex" type? I did some hours then I did my multi engine rating, which was a lot of fun, almost like learning to fly again. You could do an IMC too if you want to spend loads of money. If you do this then plan to fly regularly and practice instrument flying and approaches. There is no point otherwise.
Its difficult to keep the interest, but doing different things, and flying with an instructor again every now and then is a good idea.