The key is not to try and see a stride. As a relatively new person to jumping you will find that very hard as it takes a lot of skill. By trying to see a stride you will likely end up pushing the horse to take off long (too far away) and you will also likely jump ahead of the horse. This will put you ahead of the horses balance and make it hard for him to take a clean jump in a safe way and if he stumbles on landing you're in a risky position.
Instead of worrying about seeing a stride work on maintaining an even rhythmic stride on your approuch and waiting for the jump to come to you. You don't want to jump until th ehorse does and its th ehorse lifting his shoulders on take off that cause you as a rider to "close your angles" that is close your hip so that you go into jumping position. The horse puts you in jumping position not you. So work on getting a nicely contained bouncy even stride on your approuch and then as you turn to your jump start counting up with each stride, 1,2,3,4.....8.9 etc. It doens't matter what number stride your horse jumps on but this will help you maintain the stride you need and stop you from jumping too early. If you could down 5,4,3,2,1 and you started counting in the wrong place you will be left in the wrong place feeling like you should be jumping when you shouldn't. The worst thing I hear people doing is couting 3,2,1 from what they feel is 3 strides out. Couting 3,2,1 results in your "firing" the horse at the jump and often the horse jumps flat and takes a rail.
Anyway happy jumping and see how that works.