Juro, the main reason the discussion always start with , "get a guide" is the fact that tarpon are most often in water that is hard to get to by foot. The bottom is soft in many areas, much of the shoreline is private and hacking through mangroves is tough. Guides have boats. The second reason people recommend guides is that most people don't have a ton of time to look for fish, and guides know where they are.
I suspect that many locals or those in the know would rather not share their spots on the web.
So here goes:
1) fish the canals off the Tamiami trail. Hop out of the car where ever it looks fishy and throw in a fly. You never know what will hit. I there are tarpon in there.
2) Rent a flats boat and pole along contours in the 4-6' range. If it is clear you will see them clearly. If not, look for rolls, bubbles and water being pushed.
If you can't get a flats boat, anchor up along a likely spot. Look for points and areas that would compress schools of migratory fish.
In the back country, look for laid up fish. Bubbles, nervous water, rolling fish etc. This is especially productive in low light.
I have seen more than a few rental boats aground so pay attention to where you're going.
You could do this in a kayak, but visibility will be poor, so sticking to the back country might be a better bet for this.
One cast can change your day...maybe your life.