Also - when I hung pictures in a function room with panelling under - I lined the images up inline with the panelling too - mainly as this was a large room so was viewed from a distance. (This was in a military mess - so function room /bar / memorabilia space ) so was a bit more formal than a home - but if you apply the same ‘rules’ should help unify the look better .

Don’t you think everything is just too random? I have different frame colours and mounts, no frames, paintings, prints and photoshop? It’s truly art I’ve collected.
Initially I had the bottom a bit more in line but not totally so thank you for that tip.

It can be so challenging - trial and error. You can follow a line but with varied sizes that is not always possible. Looking at your photo some could be grouped closer together. Only rule is that there is no rule. Have a look on the web for images. Try out One Plan's suggestion of creating grouping in panels and get a friend to help you. Picture hanging strips may help you to set up a temporary arrangement before so you can live with for a few days. Good look - it is a challenge that I have yet to face once the work is done in my house!!

All your different pieces are lovely, but they don't necessarily work together very well. That, and the wide spacing between some of the pieces on the right might be the problem. The pastel coloured pieces jump out at me as not going very well with the rest. The colours and frames are different to the other pieces. Maybe they need to move away from the pieces that have the stronger yellow in it. A black or wooden frame will also help. But I think that swapping them with the pieces that are on the table will probably be better.

Maybe you can lay all pieces out on the floor first and find a pleasing composition. Then transfer that to the wall.

Found this, which might give you ideas https://www.houzz.co.uk/magazine/decorating-the-insiders-guide-to-creating-the-perfect-gallery-wall-stsetivw-vs~52790364

I think gallery walls are so difficult for many reasons. Should we equally space things so the gaps are all equal? My thoughts are that grouping pictures together so that they create a larger picture may work. Look at the image upside down to see if it helps. Asking which type of contrast dominates may also be useful. Wherever you get black and white together, that tends to dominate over colour, so black and white images or frames that are black on a white wall will eclipse more subtle artwork. I never hang anything graphic with pure black on a wall with paintings as one dominates the other. However, rules are there to be broken and sometimes things just work together for some reason. When I look at the image upside down, the I wonder if the black frames need to be separated a bit? Really difficult, I still have pictures propped up everywhere!

I am certainly no expert but my first instinct is some of the pictures are too far apart? Lovely choice of artwork though, so I would snuggle them together a bit more. That wall looks lovely.

Or you could buy picture ledges ( Ikea?) , painted the same as your wall (sand well before painting) so they disappear and have all your art displayed ... and as a bonus, you could also display little objects/ plants on them!

Yours feels a bit uniform in placement. Mine has a theme oak/wood frames but it’s more higgeldy piggeldy in placement

Try again...

Alternative

The invisible line thing mentioned earlier does work

You can also have a practice by taping paper shapes on the wall to see what the over all design looks like

I would say position them closer together. The gaps between them seems a bit more than necessary for the size of the pics. Also there has to be a common thread between the pictures. Either same type/colour of frames or a similar theme/colour (black & white,bright colours) of pictures. This I feel, makes the whole collage more cohesive.

I don't think you're far off but the pink camper is too close to the frames to its right. Try to keep spacing fairly consistent between frames. So either move the big black frame and the one below to the right a bit or get rid of the pink camper van and put a smaller one there. Also add a small one bottom left. Personally I like all black frames but that's just me