My top five: ( with maybe a few extra)
1) Get your ass to the gym. So obvious, but that is the very first step that so many guys with great intentions somehow avoid. ( I was so busy with work, my workout partner cancelled, I was tired, ect.)
2) Get good advice: Most guys don't. They get advice, but not good advice. Don't read fitness mags. They sell magazines. They feature models who for the most part are on steroids. The advice is canned and mostly useless.
3) Stick to basics. Bench press, squat, deadlift, pushups, pullups, bicep curls with a straight bar, tricep pushdowns on a cable. Too many guys get caught up in doing funky weird exercises before they even have a base. Build your base, then do single arm dumbell curls on an exercise ball if need be. Wasted time if you ask me, but no one has asked me.
4) Do cardio. If you want to lose weight, do it first thing in the morning on an empty stomache. But do enough that you can handle lifting weights. Believe me, it takes some cardio to do deadlifts.
5) Eat right. I am not a food Nazi at all, but I do not put shitty gas in my Porsche. Think about what you eat. It becomes you eventually. Don't give up fun food but make it a smaller % of what you eat. Eat smart. If you want to build muscle, eat protein every few hours, at least. Protein is the brick in a brick wall. You can workout all you want, but to build muscle, which is 70% protein and 30% water, you need protein. Working out without eating enough protein is like hiring a bunch of guys to build a brick wall and not giving them bricks. They will just stand around doing nothing. Protein doesn't have to be expensive powders and shakes. Eggs are perfect food. Eat one an hour and your bloodstream will have enough to work with.
6) Sweat. Push yourself. Don't say I am going to do X weight for X amount of reps. I NEVER count reps. Ever. Otherwise, I would say I am going to do 8, do 8, and rack it and say I did what I wanted to do. And my muscles would say, "Thanks, we handled that. Piece of cake." Every set should be taken to failure, every set, because only with failure do the muscles adapt (grow).
7) Don't think that workouts only happen in the gym. Do pushups randomly throughout the day. Curl anything you happen to be lifting a few times, a gallon of milk, luggage, firewood. Your muscles do not know the difference. Park far away from the grocery store and carry your groceries back to your car. Small, but it all adds up.
Last of all: Be active, walk, run, jog, bike, move furniture. When my friends ask me to help them move, I see an opportunity to use/work my muscles for a few hours.
8 of 10. Hope it helps.