In excel, the most used function - VLOOKUP demands 4 things - lookup_value, table_array, col_index_num, [range_lookup] which is basically - the common value, the array you have to find the data from, the exact number of the column from which you want the data and if you want exact match or approximate match.

These are some tips to avoid common problems while using VLOOKUP:

1. One thing to always remember is that VLOOKUP only works right, make sure that the column which contains the common value, is the first column of your table array.

2. After typing formule, if you just drag the formula down, make sure that you first fix the table array and lock the value by adding $ sign before the column number and row number, for example, instead of using A1:A10, use $A$1:$A$10.

3. In case you don't know your data is sorted or not, use the FALSE value in range_lookup. This would give you the exact match. 

4. If after all this you still have the #N/A issue, then remember that in excel's eyes " summarise" is different from "summarise", use the =TRIM or =CLEAN functions to solve this. 

5. If it still persists then you might have the problem of data type mismatch (like text-number mismatch), which you can solve easily by following the steps in the video above.

Bonus tip: If you create a table out of the array data, it would automatically solve a lot more time as it updates the VLOOKUP automatically.

Drop a comment down if there's any more problems with vlookup or in excel in general.