1) Make sure that the toe-clips and straps are adjusted for your style of pedaling and shoe size.

2) Ensure that you have a wrench that will fit your pedals.

3) Take them off, throw them in the trash and get some clipless pedals.

Just kidding!
I rode in straps, a few years back. This is what I did.

Reach down and loosen the strap a bit while you are sitting still, (i.e. at a stop light, etc.)
This will make it easier to get your foot in place, as you take off.
Once you get your foot in, reach down and pull the strap tight.

Of course, this I did this on a single speed, not a fixed gear, so your mileage may vary.