I would like to get some tips how you find clients for websites in your local area? - Just SEO? - Offline advertising? - Emails?
If you are looking for local clients, and are only looking at the above three options, then I vote for offline advertising. I don't know how it works in the UK, but here is the US, local radio, cable TV, and newspapers/journals have very competitive advertising options. Of course, it really depends on what you are selling, but you can get really creative and find some great local advertising deals. Beyond what I just mentioned, we have local businesses advertising on the table placemats in pizza shops or on the backs of city benches and on the sides of grocery shopping carts. A lot of options are out there.
A mixture of SEO, social media and offline. Not sure how much online classifieds are used in Poland but they are another option. SEO probably the best for specific targeting. If local businesses are looking for web design, they are going to be looking online most probably. A company local to me does very well with offline. Banners on busy roundabouts/roads, posters/flyers in high traffic pedestrian areas.