Attempting to Observe Jupiter/Venus

Hmm, I'll try that tonight if the moon isn't too bright!

Yes it looks like that the object is out of focus.or your eyepieces can't reach focus, this part is highly unlikely as your scope is designed for visual use.when I had my Newtonian OTA I needed an extension tube to be able to use it for visual.

Ah ok, I tried my best to focus it but got nowhere. I'll try again tonight but is there anything in particular I should be doing/looking out for?

What sort of eyepieces are you using?if you have heavier ones then maybe your focuser is too loose and literally can't focus as cant move the EP.just turn your focus wheels back and forth and look if the EP moves all the way up having your tube horizontally and focuser fasing up with your heaviest EP in it.
If it doesn't go all the way up it means it's too loose and you will need to tighten it.

I have:
- Celestron 10mm eyepiece
- Celestron 20mm erecting eyepiece
- Celestron 6mm eyepiece
- Celestron Omni 2x Barlow Lens

Just checked my focuser, seems to be working just fine.

Well all of them are fairly light so it shouldn't be a problem.try to focus on the moon with your 20mm as Dave suggested until you will get crisp view and then slew to Jupiter.it should be already focused and you should clearly see it along with its moons.
Now if you will see the spider vanes then your scope is way out of collimation and i mean way off as I don't know what else could be wrong...