1. Loose 和 lose
错：I always loose the product key.
对：I always lose the product key.

2. It's 和 its (严格拼写是 its')
错：Download the HTA, along with it's readme file.
对：Download the HTA, along with its readme file.
错：The laptop is overheating and its making that funny noise again.
对：The laptop is overheating and it's making that funny noise again.

3. They're 和 their 和 there
错：The managers are in they're weekly planning meeting.
对：The managers are in their weekly planning meeting.
错：The techs have to check there cell phones at the door, and their not happy about it.
对：The techs have to check their cell phones at the door, and they're not happy about it.

4. i.e. 和 e.g.
错：Use an anti-spyware program (i.e., AdAware).
对：Use an anti-spyware program (e.g., AdAware).
注：i.e. 意为 "that is"; e.g. 意思是 "for example." 二者后面都要加逗号.

5. Effect 和 affect
错：The outage shouldn't effect any users during work hours.
对：The outage shouldn't affect any users during work hours.
对：The outage shouldn't have any effect on users.
对：We will effect several changes during the downtime.
注：Impact 不是动词. 你可以考虑用 affect 来代替:
错：The outage shouldn't impact any users during work hours.
对：The outage shouldn't affect any users during work hours.
对：The outage should have no impact on users during work hours.

6. You're 和 your
错：Remember to defrag you're machine on a regular basis.
对：Remember to defrag your machine on a regular basis.
错：Your right about the changes.
对：You're right about the changes.

7. Different than 和 different from
错：This setup is different than the one at the main office.
对：This setup is different from the one at the main office.
对：This setup is better than the one at the main office.

8. Lay 和 lie
错：I got dizzy and had to lay down.
对：I got dizzy and had to lie down.
对：Just lay those books over there.

9. Then 和 than
错：The accounting department had more problems then we did.
对：The accounting department had more problems than we did.
注：当一个句子以 If 开头时,你并不需要接着来一个 then. Then 完全是多余的:
错：If you can't get Windows to boot, then you'll need to call Ted.
对：If you can't get Windows to boot, you'll need to call Ted.

10. Could of, would of 和 could have, would have
错：I could of installed that app by mistake.
对：I could have installed that app by mistake.
错：I would of sent you a meeting notice, but you were out of town.
对：I would have sent you a meeting notice, but you were out of town.

觉得很多都是容易区分的
affect 和effect有点。。