Press the tip of your tongue to the roof of your mouth, behind the front teeth.

Try to say "sler" without moving your tongue away from the teeth.

It helps if your mouth isn't too dry, a few pints of beer would help enormously.

When you've mastered that, we'll move on to pronounciation of "Llanfyllin", and "Llansantffraid".

Cheers, Bron.