A few (用于可数名词) and a little (用于不可数名词) 多用于肯定式中：
例1. I've got a few friends.  (Maybe not many, but enough)
例2. I've got a little money.  (I've got enough to live on)

而Few and little 则多用于否定式中:
例1. Few people visited her in hospital.  (She had almost no visitors)
例2. She had little money.  (Almost no money)

A lot of 常用于肯定式中：
例1. I've got a lot of work this week.
例2. There were a lot of people in the room.

搭配小结：
不可数名词                        可数或不可数名词                              可数名词
how much?                        how much? or how many?                 how many?
a little                                  no/none                                               a few
a bit (of)                              not any                                                a number (of)
-                                          some (any)                                          several
a great deal of                    a lot of                                                  a large number of
a large amount of               plenty of                                               a great number of
-                                          lots of                                                     -