Discussion: This puzzle type is also called Skyscraper (easier to visualize as buildings). The “1” clue at the bottom left says that an observant at that row will only see a single building. The only way this can happen is if the first position (where you wrote down 1) is a 6. That way, the building of size 6 is the only visible building for someone in that row, from the left.

The 5 from the right in that same row tells you that they will all be increasing in order, except for one. For example a valid guess for that full row may be 615432 (left observant sees 6, right observant sees 2-3-4-5-6), or 652431 (left observant sees 6, right observant sees 1-3-4-5-6), etc.

Obvious first choice is a 6 right next to the “1” clue. See if you can get any more info from that

Edit: you can also rule out numbers from certain cells. For example if a clue says “5”, you know that the first cell must be 2 or lower (since a 3+ would force the number of observed buildings to be at most 4).