Alright then:
1 ) Don't draw schematic symbols of chips in the same way the pins are physically arranged on the chip. This usually puts the pins in bad places and results in lots of wire spaghetti to get it connected. Order the pins in a way that makes the schematic more sensible and crosses fewer lines. The reason chip symbols have little pin numbers next to each pin is so that you can move the pins around and still know what exact pin that is. (But when it makes sense its okay like your optocopler)
2 ) If the chip you are using already has a standard symbol then use the standard symbol and don't draw it as just a rectangle. This goes for things like opamps, comparators, diode or transistor arrays, multicolor LEDs, logic gates...etc. You can use multipart components for this or stick them in a single block like your optocopler (Depends on what makes more sense)
3 ) Try to make the signals flow in a certain direction. Since most of the world reads from left to right this usually means you want information to flow along your wires from left to right. Aditionaly there is a convention that current should be flowing from top to bottom. So you want your power sources on top and ground on the bottom of components.
4 ) On the PCB you usually want to stick to 45 degree bends and straight traces where you don't have a good reason to do otherwise (This is just an aesthetics thing, makes it look more professional)
5 ) You usually want to have your ground fill on the bottom side of the board, so you can connect as much stuff as possible using long traces on the top where the components are, then jump down to the bottom layers only to make short jumpers and keep the ground fill mostly filled. But on busy cramped boards its often a good idea to have ground fill on both sides and then put tons of vias to stitch them together.
6 ) Designator placement on the silkscreen is just as important to making the board look nice. You don't want lines obscuring them and you want them to be nicely centered on the component it belongs to if that is possible(Sometimes its not due to no room). For chips you usually place the designator next to the chip body not the pins(In your case placing U1 above the chip would seam more sensible)
7 ) Use the silkscreen to mark down as much information as possible. Put down text with the name of the board, the date it was made, who made it etc... as that makes it easier to tell what this board is upon finding it 10 years later. Things like trimm pots mark each one what it does. Put text next to connectors to tell you what they are for, if there is space even write down the connector pinout.
8 ) Mounting holes. Its easy to forget about it but its often very useful to put some holes in the corners of a PCB as it makes it much easier to mount the board to something, or if its a board that just sits on a table then you can screw short little screws or standoffs into those holes to give the board feet so it sits nice and stable on a table(Especially significant if there are a lot of components on the bottom).
The user teksturi provided a really good example of what a schematic should look like