The only thing better than limoncello is homemade limoncello. Use fresh, unwaxed lemons for the very best results in flavour.
It may be preferable to use organic lemons. Try not to get any of the white pith in your limoncello as this can result in bitterness.
Traditionally limoncello is made with 190-proof grain alcohol. As this can be hard to find in the UK, in a pinch you can try substituting a high proof vodka instead, although keep in mind that this will taste different to an authentic limoncello. Look for high-proof alcohol at some off-licences or speciality shops carrying Polish goods.