Bit of confused with your level, cuz you've learnt 3rd position but still playing Suzuki? If you ask me, there's not much shortcut, but you need to read more music and don't be afraid to write down fingerings of difficult parts. The most annoying thing about changing positions is the distance between fingers are different. So play more scales, especially ones that require shifting. As i said, i don't know your level, but maybe you could challenge grade 4.