The easiest way to get there is off of Washington Street, which is the Old Town Alexandria portion of GW Pkwy. You want to turn left at the street that has Sutton Place on the left hand side (can't remember the name of the street) if you are coming from the airport.
Then just follow the signs to Jones Point. You may not find it right away (I normally miss it), but as long as you stay by the river and are heading towards the bridge you will find it.
It gets pretty packed on nice days and all you catch are BIG cats and little perch this time of year, but if you are as close to it as me, you can't beat the location.