There is no intention here to discourage you from exploring the uplands of our beautiful countryside, just to say – Be prepared & don’t take unnecessary risks.
Just realise that if you are going into the hills or mountains there are greater risks of slips and falls, the most common reason for people requiring rescuing – there can be a longer rescue time as you will be away from habitation/roads. 
Maybe 2 or 3 hours until someone can get to you.
Look at the weather forecast – take suitable clothing.
Have a plan of where you are going – let someone know, so if you are delayed or injured, the rescue services have some idea, where you maybe. 
Know how to navigate. How long will the route take – Naismith’s Rule as a guide. Will you be back before it gets dark?
You have planned your route – I must stick to it – if that route becomes unsafe – a gentle stream becomes a rushing torrent – re route to avoid the danger.
Wear suitable clothing & footwear for the conditions.  Carry an extra layer, if going higher, it can get, chilly. Plus a hat & gloves in autumn & winter.
Take a little extra food, just in case. [sufficient drink, a small bottle of Cola is not going to get you up and down Snowdon]
Carry a torch & whistle to summon help -[6 blasts on a whistle or flashes of the torch repeated at one minute intervals is the recognised signal for assistance in the mountains. ](or modern day SOS GPS locator). Your mobile phone may not have a signal, you have a greater chance with a text message. Pre register your phone –   https://www.relayuk.bt.com/how-to-use-relay-uk/contact-999-using-relay-uk.html
Carry a first aid kit – have some knowledge.
Carry a Bivi bag – it can stop you getting cold and wet, the wind can chill you down quickly, being wet, makes it worse.
Enjoy yourself, you need adventure in your life. Take plenty of breaks, enjoy the journey, getting to the top is only part of it. Don’t be afraid to turn back – “I’ve travelled all this way to get here I must finish” – the hill, mountain will still be there another day.