It is easy even on hard gwent difficulty.
look at this map and locations: http://witcher3map.com/v/#4/-79.88/67.10/m=-75.500,110.810
go around buy cards, play with this guys on the map,
you get better cards, than play with stronger players and do gwent quests.
learn how to play, that is your main problem and solution.
Once you are in Velen go to heart of stone part of the map, the win mill with two black rune merchants, you can buy nice cards there with some leaders, also go at caravan near big mansion where you go to party mission with triss, guy there sell good cards and play him as well. That way you got very strong cards, gunter of darkness and nice leaders for every deck. Also party location with ghost and medic red heard shani girl, in the barn on the leaders there is cow card, strong card as well.
Just google all this stuff and you will find it easy, than start playing stronger players.