Needless to say, smoking is even more dangerous if you have APS because it causes cardiovascular disease. Smoking accelerates the hardening and narrowing of your arteries which means that you are two to four times more likely to develop a blood clot.
Blood clots in the heart (coronary thrombosis) can lead to a heart attack and around 30% are caused by smoking, while blood clots in the brain can lead to strokes. Smokers tend to develop coronary thrombosis ten years earlier than non-smokers.
By stopping smoking, you are removing another risk factor for the possibility of developing a blood clot.
It is also important to note that, if you are taking warfarin, toxins from cigarettes and tobacco can cause your liver to work overtime to try to remove them and, in turn, this absorbs more of your warfarin (since this is processed by your liver) and therefore can result in a lower INR. So when you do decide to stop, it is important to monitor your INR for the first few weeks of smoking cessation.
If you need help with quitting smoking, the NHS provide many resources with their online Better Health service.