Hiya deanoza,
The first trick is to try and find bait that is 'fresh' and has not been frozen and defrosted several times between the supplier and seller.
Best way to establish this to look inside the box. Looking at the pilchard make sure there are no yellow/orange colour around the gills, head and nose of the pilchard. This normally means that they are old and have been subjected to being stored below best suited temp or have been defrosted.
Flip the contents of the box upside down and look for a large amount of water and blood mix frozen at the bottom of the pilchard. This normally means that the quality of the bait was not great to start off with or that the bait sttod around a long time before being frozen. Again a good sign that the bait was stored below temp or defrosted somewhere along the line.
Best baits still have alot of their original colour and markings and the eye of the bait fish is still clear. YOu can expect a white dot in the middle, but if the eye itself is frozen sunken or is milky or 'bloodshot' then the bait will be rubbish.
These are just good guides to follow and you will still get a few surprizes...good or bad! LoL
With the bait slipping down the hook...the best way to ensure this does not happen is to cotton your bait and each time you come down to the gape of the hook allow for a few good turns around the bare hook and then back up the bait. This 'locks' the bait in place and helps it from slipping down the hook.
Another good tip is to push a toothpick through the eye of your hook and leave a small section to bite into the bait and hold it in place. This measure together with fresh baits and the cotton lock will ensure a tight bait that stays in place.
Last...Shad love seeing a tail on the bait. Don't be shy to leave this section on your baits. It's very common for Shad to feed from the tail up! On bigger baits its hard to leave a tail section as your bait is then 'upside down' with the thicker section up the line and the thinner section on the gape of the hook.
This is why I like to use a trailer or Skelem hook. I build the bait body into the shank, leaving the gape clear. Then slip the trailer hook neatly between the tail and then cotton up.
Blow is a typical 'sliding trace' setup used for Shad.
another...a typical Kob trace, but showing a sliding trailer hook and the toothpick setup.