I'm not the most active chess player but I'll try to help you understand variance.
When you play chess, you probably have an opening system or opening line memorized (not necessarily consciously) that you often take. Each opening has a certain win percent against any other opening. The win percent against an opponent of equal skill in chess isn't going to be a static number. It's gonna vary based on what openings you guys have learned. There's variance there but you can minimize it by learning more than one opening system or line.
Similarly, there's variance in poker and all you can do is minimize the variance(assuming you're a profitable player you'll want to do this and if you're not keep these things in mind anyway).
I don't know what game you're playing (many variants of poker) but the concept of variance remains the same.
Keep your bankroll safe. Don't sit down on 1 table with your entire bankroll. Sit down with 1/25th of your bankroll at the maximum instead. The 1/25th number will provide a healthy buffer from downswings that'll take your bankroll out.
Consider playing multiple tables if profitable rather than moving up in the stakes. Keep track of how your profits change with multiple tables and see if it's better to increase table count rather than move up stakes. With a higher number of hands, you'll have a greater sample size and your results will be closer to the mean.
Accept that downswings will happen. No matter what methods you employ, you'll very likely have a losing session eventually. Don't let it get to you. If you're keeping track of your average wins and losses, it's easy to see if you're just on a downswing. If you're on average a losing player don't let downswings affect your play either. Try to step away from the game if you have to.
For trying to improve, CardsChat, hand discussion forums are very useful once you've gotten a feel for the opponents you'll be up against.