The higher the number, the less tax will be taken out of your pay.  So zero would result in the greatest withholding.  But there's a push-pull between withholding amounts and the tax calculation on your tax return:  the more you have withheld, the less you'll owe come tax time, and vice versa.  It's the tax return where the final tally is made; withholding is simply an estimate.

In your case, as a single filer without dependents, 1 allowance on your W-4 would be appropriate.

In addition to your W-2, if you are also paid on a 1099-MISC for side work as an independent contractor, then you may want to make estimated tax payments, since there's usually no withholding on 1099-MISC income.  Estimated payments allow you to "prepay" some of your taxes, thus reducing your bill at tax time.  You can read about estimated payments here:  https://www.irs.gov/pub/irs-pdf/f1040es.pdf.