Get an orbital sander. I hate sanding like no tomorrow but there is no getting around it. When I was in High School my carpentry teacher had me sanding forever, I hate it but I want a good project. Orbital sanders are the best for rough sanding. Use 80 grit then 100 grit and you should be good to go. No, it isn't easy, neither is the 60 foot trench, I'm digging but both need to be done. If you want something good, some things cannot be avoided.

Pressure washing is the easiest way to clean it and strip it down to good wood.

Once you pressure wash, you can sand down any roughness.

You could sand the whole thing, but it will take a lot of time. There are really any tips other than use a sanding block and elbow grease. If you wanted to invest in a tool, a random orbit sander will make quick work of the job. They are relatively inexpensive and versatile. I use mine all the time.

Something like this is good:

http://www.homedepot.com/p/DEWALT-5-in-R...

Use a sanding pad or a power sander.

Sander machine ,use with no pressure and circular movements not linear.

We recently just received a wooden picnic table n benches for our patio. However they are dirty and rugged and need to be sanded. Sanding is tedious work as it is but it's only going to get hotter. Anyone have tips for me that would make sanding easier and quicker?