How tall are you? Then we can tell you what would be a reasonable and health goal for you.
There are many fad diets out there but I don't think Weight Watchers is one of them. You can lose healthily and develop a lifestyle that works for you long term using that system. The only drawback I can see with Weight Watchers is the need to weigh foods and keep pro point tallies (which is fine if you're that kind of person - I'm way too undisciplined to do that...never counted a pro point or calorie in my life
) and a lack of a recommended exercise program (which isn't so bad - as each person needs to find what works for them anyway).
How quickly you lose weight depends a lot on many factors. In my weight loss these were my monthly losses: 9.3kg, 8.8kg, 11.2kg, 8.7kg, 7.6kg, 6.9kg, 5.5kg, 7.9kg, 4.1kg, 5.1kg, 4.1kg, 3.4kg, 0.3kg and 4.3kg. Looking at the numbers you will notice a few things. Firstly, the most significant weight was lost early on. If you have much to lose...you will lose much! Secondly, the third month was my biggest month. My muscle development was kicking in and I was now maximizing my exercise benefit. Also I was nailing down lifestyle foods choices. Thirdly, you slow down the closer you get to the sharp end of your goal weight. I was exercising far more at this stage for smaller results. Fourthly, see the poor result for my second to last month? I had lost track of what worked and began snacking too much. Basically all my mad exercising was going on burning up my extra snacking. You have got to keep focus through out or you will end up going backwards! When I started I lost 2.5kg in my first week. In my naivety I thought I could do that every week (after all - I wasn't even exercising then!)...so I calculated that I would reach my goal in the first week of September (35th week)...I was only out by 25 weeks!
I reached goal by the 60th week. Even that was extreme. Most experts believe that you should aim for a healthy 1 kilo per week. So use that number but expect to be a little better than that when you start and worse than that as you near your goal.
Doing weights is a good idea (unfortunately my medical condition at the time ruled that option out for me). Anything that builds muscle is good. Remember however to always train smart. Routine sameness is the enemy of weight loss. Vary your daily exercise intensity. One normal day; follow with a hard training day and then a light training day is better than three "normal" days strung together.
Hope you find this helpful