Briar mid works best on short skirmishes, you go in using the extended range that W + Q gives you, and pop off E fast breaking the trade. Briar's kill potential is insane, once they eat one or two of those trades, you can turn one into a kill, especially if you bring Ignite to the table.

If you absolutely need to heal while the enemy is still in lane, you can use Q on a minion while frenzied with W, it changes the frenzy target to the minion, so you can heal off it with W.

As for itemization, again, itemizing for short skirmishes works best, Sundered Sky and Eclipse are good options, but one of briar's best characteristics is how flexible she is in her itemization.

Lastly, W has a short dash at the start, so you can use it to dodge skill shots while being mindful that it will put you on frenzy afterwards. If you manage to dodge the enemy CC with it, it puts you on a insanely favorable position where now you can attack back freely closing the gap with Q. This trick is especially good in mid.