Need a polynomial time reduction from 3SAT to INDEPENDENT-SET
The simplest is to reduce Clique to Independent Set using the complement graph, as discussed in the comments.

Alternatively, you can construct a graph to directly reduce 3SAT to Independent Set using "gadgets". One possible start is to do the following: for each clause, construct one node for each of the three variables in the clause. Now, we want to place edges such that:


No two variables in the same clause can be members of the same independent set.
No two variables which are the negations of each other can be members of the same independent set.


If you can accomplish this, then for a boolean formula with $m$ clauses, there is an independent set of size $m$ in your constructed graph if and only if the boolean formula is satisfiable, thus giving the desired reduction.