Updating one table with data from another

Hey all,
There are two things I need to do:
1. Update existing rows with new data
2. Append new rows

I need to update only some of the fields table1 with data from
table2. These tables have the exact same fields.

So here's what I have currently for appending new rows (rows where CID
does not currently exist in table1, but have been added to table2):
INSERT INTO table1 (field1, field2, ...)
SELECT field1, field2, ...
FROM table2
WHERE NOT EXISTS (SELECT CID FROM table1);

But something is wrong with the logic there and I'm not quite getting
it.

For the update part, here's what I have:
UPDATE table1
SET field1 = table2.field1
field2 = table2.field2,
...,
FROM table1 INNER JOIN table2 ON table1.CID=table2.CID;

I'm not sure what's wrong with this one either.
Any help would be greatly appreciated!