You should practice in Plunder. Go to Storage Town since that's where people drop in Plunder to have shootouts. If you're trash or haven't played much COD in a while, you want ease of use guns to start with. For ARs, I'd suggest M4, Grau and Krig. Easiest SMGs to use are MP5 (Modern Warfare one over the Cold War one), Mac-10, Bullfrog and LC-10. People like using the FARA and Cold War AK-47 as SMGs too as well as the FFAR, though that's been nerfed quite a bit.
Get Overkill first so you have both your main guns right away; get Ghost on the second loadout.