Assuming you mostly have 1880-1909 coins, key varieties/errors to look for:
1886 T1 vs T2- look at the feathers and see if last feather is pointing to I or is between C and A. The T2 is slight more rare I believe. This is a variety, not an error
1888- look for last 8 over 7, supposedly very very rare and probably the king of the errors in
Indian cents1894: Look for doubled date
1897: Look for a 1 in the neck
For pre-1880:
1860: Point bust vs rounded bust- variety, not error
1864: Copper nickel vs Bronze. For the Bronze, there are two varieties: 64 and 64L. The 64L is much more rare. If you can't see the L (have to turn coin 90 degrees at back of the head where the ribbon is), you can tell the difference between the no L vs L by the bust- 64L has pointed bust, 64 has rounded bust. The three major 64s are varieties, not errors.
The other thing to look for on the 64s is doubled dated. I have a couple in my collection
1865: the 5 can be plain or fancy- variety, not error
1869: 69/69 doubled date. This one is tough and is often missing in complete colelctions sold on
ebay.
1873: closed 3 vs open 3- variety not an error; also doubled "Liberty" (very rare, in part because most 1873 are worn down too far to even see "Liberty")
There are many minor varieties/errors, but I don't have enough knowledge on those.