Every matchup is different. Generally speaking you have 4-5 major threats in neutral, which should be abused in different ways in different matchups. You also need to learn how to combo/punish each character once you have landed your first hit.
AC fair. If you execute properly you can create a high priority hitbox wall while fast falling, but still auto cancel the move before you land. This means you don't even have an option of failing an lcancel, you just have no lag (okay, 4 frames; same as empty landing). One of the safest moves on shield, it also is very difficult to wiff punish.
Immediate nair. This is a 3 frame aerial with a ton of priority. It is faster than grabbing out of shield, and it auto cancels in a short hop. Fullhop nair also auto cancels onto platforms. Its very safe, does a good amount of damage, and lets you get your shield up quickly.
Grab. This is the one everyone wants to land. Virtually everything sheik can do can be CC'd at low percents, except grab. Grab also leads into more grabs (either by tech chasing or true chaingrab) or a guaranteed aerial. Because its so rewarding, your opponents must spend a lot of effort avoiding it.
Dash attack. A quick attack with a burst of movement, acts as a launcher. It doesn't knock over until about 40% and can be true CC'd until about 60%. It is also really unsafe on shield. Really only good for calling someone's bad movement.
Fullhop bair. Tons of range and acts as an anti-air. It is a perfect tool for covering side platforms and controlling the middle of the stage. It is also relatively safe to land with bair, but not as safe as AC fair.
