Ward one side of the river and stay near that side when CSin'.

"How to know your gonna survive in a 1v1"

Play one champ a lot and you'll get a sense of when you can win a 1v1.

Pay attention to enemy champ power spikes, thier item builds, and rune/masteries.

If you're starting out fresh DON'T try and main a skillshot dependent champ(Xerath) you'll do no dmg.

When to Roam?

Assess the situation roaming is about understanding Risk/Reward. If get no kills for example you'll fall behind in CS and EXP if the enemy mid doesn't match your roam. Generally you want to push in your wave(clear enemy wave as fast as possible) and get priority. Communicate with your team about possible ward placements and enemy jungler location. The key to a good roam is good communication and understanding where everyone is on the map.

For example if you show up bot and the enemy jungler comes but your jungler is top you're not creating an ideal scenario for success. You want to have a numbers advantage and get kills before anyone on the enemy team shows up to help.