1st of all: Welcome to our family!
Not bad for your first ones. I remember the old days when i started chopping...anw back to the subject. When you are searching for rims try to find bigger resolution images.. Try to find those rims in the same angle as your car because if u can see on Lupo the rims are flat..so to add extra realism and look like the rims are in 3d like u need to do as i advice u. Also please play a little with brightness and contrast to make the rims one with the "Before" picture if u know what i mean.. (don't have a bright car and dark rims as example)
3rd: When u are lowereing the car try to not leave those double lines on the top..(try using the history brsuh or add a black line if you want to stylish your final image)
4th: It's difficult i know for the 1st time but try to learn the pen tool for better selecting anything u want to edit.
5th: I can see on the Golf 4 you made that u erased the logo and lisence plates.. Not to bad but you need more practice to add some realism again.
Good job shaving the handle though and the plastics on the side!
6th: When u lower the car, the wheels need some shadow underneath the side wing to add some realism. And also it plays role how you will make that shadow, u have to see the lighting on the Background and then think how u will make it!
7th: Another big mistake is that your rims are not in the correct place. Try not to use the same rim and also when u are replacing the rims u have to transform them on the same angle, height e.t.c so it will blend with the wheels..
But for the first time thats good.. Advices that i can give u are:
a)Practice
b)Read tutorials "How to" (In the forum we have a lot of stuff)
c)Take your time
d)Realism is what we need (if u can achieve that then u will learn a lot and be better and all your chops will go to the next level)
e)Practice
Now that's why they call me the Champ. LOL
I know i told you to much things but i felt that way man...
AAlso please forgive me if i said something that u can not understand but it's 3 in the morning!