I'm not a "professional player," but I've been playing for almost two years. Here are some suggestions to make it easier and seek help to buy league accounts:
There are three levels of runes. The first is available from the start, the second when it reaches level 10, and the third when level 20 reaches. It's a waste to buy runes of level 1 or 2, as they will quickly reach level 20 the runes. So you better start with the free champions at the beginning and save your IP for the runes. If you have enough IP to acquire at least one Level 3 page, you can purchase additional champs that you want to play. Note that it is not possible to sell champions. So it's best to try the champs first to avoid disappointment.
Since LoL can play for free, there are also some annoying types. Fortunately, there is a "mute" feature that silences them. So do not join the flames warfare if you find them, reduce them to silence and play in peace and harmony!
While you are new, you should buy the recommended items for each champion. If you have more experience later and would like to try out new designs or item tactics, aussyelo.com has excellent guides for each champ. I always visit here before I try a new champion. Once you feel comfortable and safe, you can also visit the numerous programs and see how professionals play. I recommend to not do it before level 30.
Many experienced players have LoL smurf accounts today. It means that at your level you will often encounter enemies that have far more experience than you and kill you easily. It is very annoying, but once you've crossed level 5, the Smurfs will be less. And remember, if someone calls you, shut up and keep going.
I strongly recommend playing the tutorial and training for everyone in combat as the basic tactics explained here pretty well.