I think honesty is always best .
We all work to uphold and/or improve our place in life . Any logical person would understand that , if not then they probably aren't the right people to be working for to begin with . If your an asset to the company then it's likely that they'll offer to sweeten your conditions .
A typical notice is 2 weeks but it's not carved in stone . If they are in a bind then a months notice is respectful and usually appreciated ( if that is possible ) . The last place I worked got a months notice and me popping in to help with projects at a premium , other places got 2 weeks and some I've walked out in the middle of the day . It all depends on the people .
On the flip side , pink slips usually come without notice when things get slow