As mentioned, you need quality ingredients to start with. Greenalls is a pretty bottle, it kinda stops there.
Current favourite is Portobello Road and fever tree, Highball glass, maybe a double shot to a can, three clear cubes of mineral water ice. Ooh, get me! Slice of lemon for the traditionalist. I would recommend Bombay Sapphire as an introduction as it's quite floral, it disguises it's "gin-ness" rather well.
Northam Saint is right about FT, but Schweppes has a unique zing to it.
edit, having drunk gin for a quarter of a century, I've never tried sloe gin. Recommendations?