When i lift heavier weights when squatting i am arching my back too much. This guy at my gym told me to point my elbows outward, but this makes the bar unsteady (i dont want to drop it).
Any other advice to help me keep my back straight?
Use a weight that allows good form, gradually increase the weight over time.....if you're arching excessively, it is better than getting folded in, as it is something that can be corrected mentally, rather than a weakness.
Have you thought why you're doing it. Is it just anxiety at the weight or an indicator of a weakness you have? Are you new to squatting? Do you squat deep Oly syle or PL style or, maybe, stop above parallel?
Following biggt's advice is the first thing you should do. You're unsure of the mechanics of your form somewhere along the line. You'll not be able to figure it out as fast using maximal weight and you'll likely ingrain some bad habits. Nothing wrong with slowing things down. In the meantime, go to the library for some BB books or search on-line for a tutorial. Some guys have a harder time than others getting it down. If all you do for several weeks is light weights but good form you're still going to be better off.
Have you thought why you're doing it. Is it just anxiety at the weight or an indicator of a weakness you have? Are you new to squatting? Do you squat deep Oly syle or PL style or, maybe, stop above parallel?
I think i do it because i dont want to drop the weight. It seems secure if my back in arched a bit. I squat parallel. I think my back is also not very strong. I have been squatting for about 6 months.
If you're stopping at parallel and not using a PL style technique (very wide foot spacing and keeping the shins almost vertical) then you might consider reducing the weight, maybe a lot for a while, and going all the way down deep. It could help significantly to strengthen your hamstrings and glutes which will lead to a lot more stability.
It could take a month or two before you're back to your current squatting weight but you should be better able to cope with the stresses when you do get back to it.