1. Have you organized your supply?

For a period of time transit through the Channel may take longer than usual – might be good to anticipate with some inventory

2. Get ready for a change in product registration requirements

If UK exits the EU, specific rules for product registration may apply.
You would have to get registered through a UK authorized representative for products sold in UK, and products made in UK for Europe may require similar registration work through a EC Authorized representative

3. What about brand registration ?

International or Madrid Protocol Trade Mark Registrations (WIPO) will still apply to UK, and UK will still be part of the designated states of WIPO Trade Mark
In case of no deal, UK will provide an equivalent trademark for already existing registered European Union Trademark, with a specific prefix designation. This equivalent trademark will be granted at no cost, but renewal of it will fall under new terms specific to UK market.
In case of a deal, an extended period running until end of year 2020 will be given for the creation of the equivalent trademarks, as per negotiated transition period.
A 9 months’ window to re-file has also been put in place for trademarks which are pending renewal. No notification of the expiry of that 9 months’ period will be made by UKIPO, and processing of the renewal will be charged the price of a new UK application.
Because renewals can be posted 6 months prior to renewal date, it can be interesting to initiate renewal earlier to still benefit of the cloned UK registration without paying a renewal fee.

4. Domain names

.eu extension will not be available anymore to UK residents or organization established in the UK