First off, I suggest going into options and switching your relic activation to Button mode so that you only have to tap
to use relics rather than having to use the left thumbstick/d-pad and button combo. It makes the entire game much easier IMO.
There is a spot on the Pridemoor Keep stage that is fantastic for knocking out quite a few of these miscellaneous achievements. You'll reach a checkpoint with several of the flying enemies right at the checkpoint location. Using this spot, you can knock out multiple achievements. I suggest coming back after you've gotten all the relics so that you can use the Phase ability to group the enemies together better, then switch to the appropriate relic for each achievement. Leaving the checkpoint/enemies screen and re-entering it will respawn the enemies, and if you run out of magic you can simply commit suicide in the nearby pit to refill.
For Flare Wander, kill off the first group of enemies near the checkpoint. Head to the right and jump across the first pit so the screen starts to scroll right, revealing an enemy. IMMEDIATELY run back to the far-left side of the screen and fire a shot straight to the right. It should hit the enemy just as it comes onto the screen to follow you, unlocking the achievement.
In the interest of creating as much of a one-stop-shop as possible, I've included 22 of the miscellaneous achievements in Shovel Knight in the video below. I wanted to include Knuckle Down as well, but the stage for that was already complete in my game and I haven't played back through again to unlock it. You can see Flare Wander at the
17:56 mark.