4 answers
That's really easy to do. First you want to go into your Visualforce pages and make sure they are enabled for Salesforce1 Then you have a choice. You can use the Custom Button approach that will be available in both Classic and Salesforce1 / Lightning Experience but you cannot set the icon for this. To do that you just goto Setup ⇨ Customize ⇨ Leads ⇨ Buttons, Links, and Actions ⇨ New Button or Link and fill out the following
Your other option is to add it as a Visualforce page action. This will only be available in Salesforce1 / Lightning Experience but you can customize the icon.
Then once you have your action / button created you add it to the Salesforce1 and Lightning Experience Actions section of the page layout
If you want it for classic you'd also add your Custom Button there.Then you're good to go and you'll see it in Salesforce1
You can also do both a button for classic and an action for Salesforce1 but it's a little tough to tell them apart (without trial and error) if you give them the same label.
