lilTanker saidyeah it might be obvious, depends on how you take to it...
I was worried about that my first time. I had come out just 3 weeks earlier, and joined a gay local BBS in Seattle (non-Internet, direct dial-up). Tried to hook-up guys from there because I couldn't wait to have my first gay sex, and didn't yet know the Seattle gay scene, but was embarrassed to tell anyone I was a virgin at my age. Fortunately this one guy said he only wanted oral, no anal, so I figured I should be able to handle that and picked him.
I arrived at his place on my motorcycle more than a little nervous. He brought me inside and we sat on his sofa for a long time making small talk, me not knowing how to get things started. The entire story is kinda funny, but staying on the topic of sucking dick, we finally ended up in a bedroom, where he blew me first.
He had fantastic technique, as if he read Tanker's post here, which is golden advice the OP should follow. His suction practically turned me inside out, and he hardly bobbed his head, letting his powerful tongue and suction do all the work, and I couldn't feel his teeth at all. He kept it up even as I started to cum, which seemed to go on forever, and it remains to this day the longest and most intense orgasm of my life. Of course, being my first gay sex was a factor, too, but he was also very, very good.
So now it was my turn, and I had 2 worries: would I freeze at putting my first dick in my mouth, and could I do it well enough that he wouldn't know I was a fraud, and not experienced at all. So I tried to copy what he had done to me, since I figured most men will give oral sex the same way they want to receive it themselves. Plus I added a few likes of my own. And BTW, I took to his dick like it was candy, found out I really crave those lovely things.
Afterwards he complimented me for a great blowjob, making me just beam with pride. We saw each again over the next few months, becoming fuck-buddies, until he got a job transfer out of the area. I learned a lot about BJs from him, and have tried to keep learning ever since. Practice makes perfect!
So yeah, it's possible to do well enough that it's not obvious it's your first time, especially if you can arrange to have him blow you first to get some pointers on what he's gonna like for himself. Because when you're sucking a guy it's mainly about him, so pay attention to the clues he gives you, the things he says and the sounds he makes, the way his muscles tense, and the other signals he gives that tell you what he likes and doesn't like.