hey man the marker rendering isn’t bad for your first shot at it. however, i think you should scale back what you render. cars are very complex forms just to get the linework down, and even more complex when you try and render the color in, because then you have to deal with shading, reflections, so on and so forth. the orange background looks sloppy only because you have that horizontal line suggesting a box; it wouldn’t have looked AS sloppy if it was just the vertical lines. the reason why you shouldn’t use that kind of a background with this type of sketch is the sketchyou have here has a tighter/cleaner feel to it, so to put in a background that is messy doesn’t fit. i’m not saying the background never fits and dont ever do it, you just have to (and you will learn) when to implement that kind of a background. and often different colors of markers dont mix well together, as you tried to do on your glass shades of grey usually blend very well, but colors…not so much. (at least from my ability…maybe i just need more practice lol). also i notice you try and shadow places with your pen that you then try and shadow with your marker. for that, pick one or the other. in this case, you don’t need to use your pen to shadow if you have a marker to do it. that cross hatching usually comes in handy when you are just using your pen/pencil/etc. for the most part you made your marker strokes in the same direction which is good. just remember that probably 90-95% of your strokes should be in the same direction. the only time you could go another direction is on the borders of objects, but even still try and follow the same direction because the markering you just did won’t bleed together as well.
since you aren’t asking for a perspective crit i won’t give it, but just a little commet: for the most part it’s on, there are just a few parts on the car that don’t quite match up.
for marker practice, i would say to just focus on the cool or warm grey sets for shading so you can get the idea of how markers work, feel, and interact with different mediums, as you’ve found bristol board doesn’t look all that fantastic for markers personally i just jack some printer paper from wherever i am and use that. if you really find you love rendering with markers, get some real marker paper. canson marker paper seems to be very popular and works well. here’s an image of it so when you go to the store you know what it looks like http://www.plazaart.com/images/2146/Canson%20Marker%20Pad%20LG.jpg
i also want to comment on your line work too. practice on your line work even before you get into marker rendering. don’t be afraid to show us a wire frame sketch and your construction pieces. a lot of times that gives the sketch more interest and life. as far as line weight, generally your line should get thicker around shadows and thinner around highlights. when i look at your sketch, the one really bold area is from the top of the windshield to like halfway down the right rear bumper, which doesn’t make sense. i realize you are trying to show a separation from your background, which then should tell you the background you chose isn’t right for the type of sketch.
if you read none of this post (lol i know it is long) at least read thisscale back what you render and just for now be concerned shading objects with cool or warm grey markers sets, just so you can practice getting the feel of how markers work. don’t worry about fully rendering objects just yet.
hope this helps – feel free to PM me