By picking Enchantress, you give up any semblance of relevance in the late game in order to have an absolutely brutal early game. You are never going to be as dangerous past minute 20 as a Shadow Fiend, simply because of how your skills work. So if you pick Enchantress, it needs to be because you are confident you can ruin your lane for your opponent. You should be able to out-last hit, out-deny and out-harass him, all the while being basically invulnerable due to the combination of Untouchable and Attendants.

• Go train last hitting. Aim for 50 cs before the 10 minute mark as a minimum, not counting denies. Don't rely on kills for gold.
• Speaking of which, denies are important. In this matchup, you outrange, outspeed and outdamage SF - ideally he shouldn't get any CS uncontested. If he does get CS, make him use mana for Razes.
• Hit him. Your amazing harassment ability comes from being able to right-click him with impunity. He can't trade with you because of Untouchable and Nature's Attendants. You should be able to force him out of lane with just autoattacks.
• That point in Enchant is a waste. Bringing a creep to lane is decent but you don't need it. Slowing him is nice but you don't need it. You already do more damage and run faster than he does. Put points into Q and E so that you're harder to kill.
• If you're doing your job right, SF will retreat to the jungle to stack and farm. Follow him. Keep up the harassment. Your entire job is to set him far enough back that he never recovers. Kill him, or drive him away, then farm his jungle.
• Keep an eye out for ganks. Chances are, SF will start bleating to his team for help - this is only an issue if they have magic burst or lots of stuns. Try not picking Enchant into these lineups, but if you do, be prepared. Watch the minimap. Cast Nature's Attendants ASAP.
• As the game goes on, you will fall off. It's unfortunate but inevitable. Don't play the rest of the game with the same "fuck you" mindset you play the laning phase with - get Aghanim's and some support items, focus on standing well back and landing heavy Impetus hits, and Enchant a useful aura creep (like the Alpha Wolf) to buff your team.
• Remember - YOU CAN'T RAMBO THE REST OF THE GAME. Your skills give you a huge early advantage, but that natural advantage will evaporate. Hopefully in that time you've made life very difficult for the enemy and amassed your items, but there will come a point where you're suddenly a very squishy walking ult and Q and E don't do fuck all. Know this and respect it.