I have just completed week 9 and am hoping to stay focused by doing a local Parkrun in a week or 2. I have looked at the course and the course seems to be a miz of gravel, tarmac and grass.
I have thus far only run on pavements and pothole filled roads. Will I find the change to a multi surface run difficult and do I need to do any particular training for it? Any advice would be greatly appreciated.
One of the Parkruns I do is on grass and some tarmac paths, the other one is through woodland so compacted earth (sometimes mud, if it's been raining) and gravel. The latter is my favourite even though I tend to come back with wet feet and muddy socks. I normally run on pavements and don't do any additional training for the Parkruns but other may take it more seriously than me.
You'll probably find the parkrun easier on your feet than pavements and roads - though if it's been wet, make sure you've got a bit of grip on your shoes, not like me last week with almost gripless shoes sliding around in a slick of mud!
I went to look at my parkrun route (I downloaded a map from the website - it isn't marked as a parkrun on the ground except Sat mornings) and did a couple of test runs before I did the Saturday one, so I had an idea of how long it would take me (ages!), as I knew it had a steep hill in it, and I'd not run up hills before. A flat route would probably be fine though.
I'll definitely go again - haven't decided yet whether to wait a week or two or not.
My local one is around the edge of the park on grass, a very short piece of pavement (bliss)then alongside the lake... Last Saturday was my first, and I was ankle deep in mud, fell over in it too; had aching muscles for a few days that I didn't know existed from the slip slidiing sideways... but everyone was friendly and helpful, especially the volunteers who had to wait for me bit still cheered me on!
I will be going again, but debating this Saturday only because of the mud - sort of tempted to try Chelmsford as it looks like it may be less muddy, but not decided yet as I should catch up on sleep as going from earlies to 12 hour nights on Saturday,,, Decisions! 
I think the biggest thing about parkrun is it being an organised run, I can't see the surface is such a deal.
I find our pavements have cross slopes for drives and lumps from tree roots so aren't as even as you would think. On a Parkrun people have sussed the easiest route through any hazards so you can follow the pack.
Main thing about a Parkrun is the friendly atmosphere. Give it a go!
Test drive it beforehand, oh that should be test run it!!! You'll have loads of fun and meet lots of like minded people, so just get out there and give it a go. Good luck.
Pavement running 
Outdoor run on the pavements rather than over the park 😔
Thetford Parkrun - a very wet affair!
