If you entered all of your contacts in your Samsung phone as Google contacts and not phone contacts (highly recommended) then all you have to do is sign in to your LG phone with your Google account and the contacts will transfer automatically.
If you kept them all as phone contacts, you will need to go to your contacts app, press the menu key, choose "import/export" then choose "export to SD card". Put the SD card in your LG phone, go to contacts, choose "import/export" and then choose "import from SD card". Select the CSV file you just created.
My personal preference is to always keep the contacts on a google account. Then I don't have to worry about transferring phones.
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