CF - he only has a lot of options at specific ranges, and most/all are beaten by one or all of ftilt, fair or bair. It's a match up I feel you need to play a lot to get the hang of, especially with all his weird movement.
Spacies - dealing with shield pressure is a matter of patience and practice. Your best options tend to be SH Nair, rolling or WDing OoS, though grabs can happen if you see them make a mistake. If they are doing their aerials late, then wait until after the shine to act. Conversely, if you see them hit your shield well before they can land, you should be able to hit them with a nair or escape before the shine can happen. So long as you trust your shield and keep your cool you should be fine.
Dealing with falco's lasers is a pain. Moving around them with platforms, jumps, dashing under high lasers, power shields and WDing out of shield takes a lot of practice. However, so long as you have experience in what lasers can do, you will find they aren't that great, though they do control a lot of the match up. Fox's lasers are just damage racking, so keep at a distance that if they start firing lasers, you can punish them for it.
Damage racking is tricky due to that crouch cancel. However, sheik's dthrow leads into a great tech chase where you can regrab repeatedly if your reflexes are good enough. That is a whole topic to itself though. In general, use needles, spaced aerials and grabs until they are out of crouch cancel percentages, when your options drastically open up.