If your balance sheet is a relatively simple one, and you have very little or no debt, then it may be fine to simply use a trusted online resource. More complicated wills usually require the help of an attorney who can help you and guide you through the process.
Be warned though: hiring an attorney will not be cheap, but it may very well be worth the cost in the long run.
Do I Need Professional Help to Prepare a Will?
How Much Does it Cost to Prepare a Will?