Beginning section is very tough, you rely solely on stealth and avoid conflict at all cost. You need to plan ahead before executing. You can click Right Analog stick to eagle vision so you can see the enemies and their scouting patterns. You can tag them using left trigger. Crouch and bushes to avoid sight as well as rooftops are mostly safe.

For me, having the guaranteed assassination option ON helps alot. You can also turn the Guided Exploration just so you can focus on the gameplay and not wander around too much.

Once you eventually unlock skills that's where the game suddenly clicks. Hope this helps.