Not thinking about it can be hard, yes. My best way is to stay in the present moment. For example, my most recent manifestation was to meet a soul mate. Not any soul mate but the one that I can be in a more intimate relationship.
What I did was to manifest 3 days straight, thinking mostly about that then I just focused on my work and daily life.
What is most important for proper manifestation is to convert the thoughts into emotions and if you really have the concentration you can create a cycle. A thought creates an emotion which creates another thought, which creates another emotion and so on. Visualization really boosts everything but be sure that you're not being specific. For this one I've been visualizing a silhouette of energy but no specific body and face structure, which leaves the doors open for all possibilities.
I personally have mastered manifesting events and I find myself doing it during most of my day. I want to meet someone - I manifest it. I'm impatient waiting on the line in the store - I manifest it going quicker (don't ask how, I just feel it and it happens). You can say I've learned to build my days, which actually makes you walk on a thin rope with one side being manifestation and other - control obsession. I've learned this the hard way.
Anyways, I'm now working on manifesting items and financial abundance. I'm not really good at that and my only guess is that the visualizations should be more specific, but should I manifest the items I want (house, car, maybe a yacht

) and wait to be guided on earning the money I would need for them, or I should focus more on money itself? By now, I've manifested events that lead me to learning new skills that could possibly get me some cash and that came useful. However, I would like to explore other methods, so any tips will be useful.
Sorry for the long post

Thank you! I hope I'm being helpful.