Hi Gary,
Don't do motorsport, but I do quite a few portraits... Here's my process :
1. Set up 2 filters. One to hide rejected photos from the library and one to show
only rejected photos in the library. Set the filter to "Hide rejected"
2. Go through each of your images individually in Loupe Mode (quickly) checking for & rejecting (press X) obviously blurred shots or terrible compositions (i.e. Things I Tried That Didn't Work). As you press X, the photo should disappear.
3. Back to Grid mode. TAB to remove the end panels (TAB again will bring them back), and also remove the top panel. Leave the filmstrip.
4. You're likely to have photos of the same style close together. Start to group your photos. Shift/Ctrl+Click a group of similar images and press "N" to go to Survey mode. This will give you a nice big bit of screen space to look at them. Select & press X on the keyboard to reject the duffers. Press the little cross to remove the photo from Survey but keep it in your library. Start with the most obvious photos and whittle things down. You'll see that as you reject/keep the obvious photos, the less obvious will grow and fill the space. Once you've done a group, press "G" to go back to grid mode and select another similar bunch.
As to "which to keep". What do you do with your photos? Are you making a book? Selling them? Putting them on Facebook? Instagram? How many do you need from each shoot/session?
The portraits I do for my wife end up on Instagram and she likes 10 photos for each makeup "look". I keep one shot of each similarly composed image. Looking at my example above (counting L-R, I'd pick one from 3 & 4, one from 6 & 7, one from 8, 9 & 10, and one from 11 & 12) because they're similar. I'd probably end up deleting 1, 4, 5, 6, 7, 9, 10 & 11.
I don't do motorsport, but just briefly looking through your Flickr, I see a green post that's popped up in a few images obscuring your cars. I'd get rid of those. Ones where you haven't got the whole car - get rid. If you've got 20 photos of different cars coming round the same bend - group them all together and put them in Survey mode (shift click them all in the Library mode then press "N") and whittle down to 10% of what you started with (from 10, pick 1). If 10% is just too harsh, do 20% (keep 1 in 5). However if you're selling photos of drivers, you need to keep one of each driver coming round the same bend. But as a spectator, this doesn't make for an interesting image feed.
Once you've finished, deal with the photos you rejected. I delete mine from disk, but if you're not confident, you can just remove them from the library and keep them on disk. (Use the filter to show "rejected photos only", shift+click to select them all then delete!)
Self-critique is a good skill to have. If you feel you're weak at it, you need to find someone who will help. Contact Sheets were how we did it in the olden days, and Survey Mode is Lightroom's answer to it. But there's nothing stopping you printing out a contact sheet, or making a jpeg of it and putting it up somewhere for people to pass opinions. Finally, if you critique others' work, this will also improve your own ability to self-crit. Magnum's "Contact Sheets" book is a fab resource too for seeing how professional photographers whittle down a roll of film to 1 or 2 exposures that they kept.
Hope this helps. Probably went on far too long for someone who knows nothing about motorsport! But Survey mode in Lightroom is awesome and makes culling a doddle.