A lot (meaning more than a few) is always two words. The phrase is often misspelled as alot. Allot is a verb that means to distribute by lot or shares.
Accept means to receive, or agree with; Except means to omit or to exempt. The two are commonly misused and often interchanged at little cost to standard usage.
Affect & effect are two highly misused and interchanged terms. As a verb affect means to influence. Effect as a verb means to cause but as a noun means result.
All right is always two words. Alright is not a word, although like altogether and already it looks like is should be and spellchecks are strangely allowing it.
A crepuscular animal is mostly active during twilight, which is at both dusk and dawn. House cats, bats, bears & ocelots are an examples of crepuscular animals.
An em dash (—) is slightly longer than an en dash (–) and both are longer than the hyphen or minus symbo (-). Typically the em dash is used like a comma.
It's and Its are often misused and confused in written English. It's means it is while its is the possessive pronoun meaning something belongs to something.
A landlubber is someone who has no knowledge of boats or the sea. Lubber (noun) referring to a clumsy, lazy, or all around inexperienced person with boats.